Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/48—Suction apparatus
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/48—Suction apparatus
  • D21F1/52—Suction boxes without rolls
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F9/00—Complete machines for making continuous webs of paper
  • D21F9/003—Complete machines for making continuous webs of paper of the twin-wire type

Definitions

• This invention relates to the technical field of the pulp and paper industry, especially to the Fourdrini process of laying an aqueous suspension of fibers on a Fourdrinier fabric and dewatering and drying it to a sheet of paper.
• Modern paper making processes and ' machinery follow the Fourdrinier method wherein an aqueous dispersion of paper making fibers is poured onto a high speed travelling woven fabric through which water from the dispersion drains leaving a thin web of wet fibers which is dried and finishe to a sheet of paper.
• the key step in this method is that of forming the web from the fiber/aqueous dispersion. This must be done very quickly and uniformly across the width of the endless fabric. Normally, the transition of de- watering commences by gravity, followed by other means such as foil blades, continuing with a plurality of con ⁇ trolled low vacuum boxes and then by a plurality of high vacuum boxes. There are many causes for mishaps to occur that prevent the final sheet of paper from being perfect.
• Another object is to decrease the amount of friction between the fabric and the dewatering components to increase the fabric life.
• a further object is to substantially reduce the length of the forming area of the Fourdrinier fabric, thereby reducing the number of dewatering components required.
• one submerged drainage box in accord with this invention may replace 20-25 foils of the prior art and in substantially less space along the length of the fabric.
• An additional object is to improve the sheet formation by decreasing its porosity and substantially elim ⁇ inating pin holes through the sheet.
• Another object is to decrease the power consumption of the Fourdrinier machine in both driving the fabric and by eliminating high vacuum pumps to supply suction to the dry end flat boxes thereof.
• Yet other objects include:
• Surface Tension is a condition that exists at the free surface film of a liquid by reason of intermolecular forces about the individual surface molecules and is mani ⁇ fested by properties resembling those of an elastic skin under tension.
• Surface Tension is a characteristic of the water meniscus which can be modified by chemical means. The meniscus changes its geometric (concave) shape depending on the size of the vessel containing the fluid. In capillary tubes the meniscus reaches extremely high levels of energy in the form of pressure. The resistance of the meniscus to rup ⁇ ture, compared to its thickness is very high as is well known.
• Draining under Meniscus or Submerged Drainage is a water removal operation whereby water is removed from the aqueous dispersion or wet web by means of a reduction of pressure originating from, and transmitted by the water it ⁇ self and not by high vacuum as may be provided in the drier end of a Fourdrinier fabric.
• This invention relates to a submerged drainage system for removing water from a moving Fourdrinier fabric having a drier end downstream of a wetter end, an outer surface, and an inner surface in a paper making process.
• the improved system includes a first plurality of spaced elongated sta ⁇ tionary drainage boxes each having a bottom and an upper drainage surface in continuous sliding contact with the inner surface and an aqueous dispersion of paper making fibers sup ⁇ ported on the outer surface.
• the drainage boxes are spaced along the wetter end of the fabric and each has an internal space for containing a volume of water extending to and in contact with the inner surface of the fabric.
• a plurality of passageway are provided from the drainage surface to the in ⁇ ternal space of the box to conduct water from the outer to the inner surface of the fabric to the internal space of the box.
• a first passageway conducts water from the space by gravity outwardly of the box.
• volume of water within the internal space induces enhanced drainage of water from the aqueous dispersion.
• An important aspect of this invention includes means for maintaining the level of water of the internal space of the drainage box constantly in contact with the inner surface of the fabric to inhibit the formation of an air water men ⁇ iscus from being between said inner surface of the fabric and the upper drainage surface of the box.
• the system further includes is a second plurality of spaced elongated stationary drainage boxes along the drier end of the fabric and having a drainage surface in continuous contact with the inner surface.
• a web is formed prior to the drier end from the aqueous dispersion of paper making fibers supported on the outer surface above the boxes, each drainage box including a plurality of cells each having an internal space placed under subatmospheric pressure by a fan means for each cell extending to and in contact with the inner surface of the fabric.
• a first pas ⁇ sageway conducts air from outside the box to the drainage surface of the box and the inner surface of the box to the internal space of the box and the first passageway through the interstices of the fabric.
• a second means applies a small vacuum to the internal space to modify the natural tension of the meniscus of the water in the fabric to induce drainage of water from the web to the fabric and the box. Also, a means is provided to discharge the water from the in ⁇ ternal space of the box.
• a means for applyin a vacuum which may include a vertical head of water having an upper surface with air under subatmospheric pressure above such surface of the head of water.
• a means to control and maintain constant the level of water in the internal spaces of the first drainage boxes is provided.
• the first passage ⁇ way of each box includes an exit conduit for water to flow out of such drainage box, and a movable valve to open and close the conduit.
• a float may be placed on the surface of the vertical head of water, and means to sense the position of the float or the pressure of the volume of water in the box, and correspondingly to move the valve to open or close same in accordance with its position so sensed, may be lo ⁇ cated adjacent the float. This is accomplished in one embodiment by a source of electrical and fluid power and in another preferred embodiment by mechanical and fluid power.
• the upper surface of a volume of water is in contact with the Fourdrinier fabric as it passes by, and water is removed from the aqueous dispersion of paper making fibers resting on the fabric by controlling the outflow of water from that volume so as to produce a differential pressure, as by it flowing into a tray at the box bottom and outwardly therefrom.
• a vacuum over a vertical column of water is controlled so as to cause a suction to be applied to the volume of water to place the meniscus of water in a pretension condition to cause contact with and with ⁇ drawal of water from the aqueous dispersion.
• water removal is effected in two directions from the dispersion by employing two Fourdrinier fabrics, one above and one below the dispersion, and causing water to flow out through both fabrics.
• each box includes a plurality of spaced parallel blades with a forward area in contact with the fabric and a rearward area being relieved to enhance de- watering of the dispersion on the fabric thereabove.
• Air suction tubes may be spaced along the length of the box to remove air and water entrained in the water in the fabric and therebelow. Such tubes are connected to an exhaust fan and a water discharge leg is connected therebetween to discharge water into the outflow of water from the boxes.
• each cell having a nose with a horizontal planar surface over which the inner surface of the fabric slides.
• the first passageway is at an acute angle with the planar surface to conduct air into the inner surface of the fabric in the same direction as the movement of the fabric.
• the second passageway is at an acute
• SUBSTITUTESHEET angle with the planar surface to conduct air and water away from the inner surface of the fabric into the internal space thereby minimizing any air being passed through the web.
• a source of steam preferably is used to heat the air passing through the first passageway to enhance water drainage from the web.
• the invention herein is also seen to include a method of removing water from an aqueous fiber dispersion supported on the fabric including sequentially passing the fabric and the dispersion over and in contact with an upper level of a volume of water enclosed on all sides except for the side in contact with the fabric; removing water from the volume of water at a level below the upper level to produce a differ ⁇ ential pressure effect on the volume of water; controlling the removal of water and the differential pressure effect to achieve an optimum dewatering of the dispersion uniformly over the fabric as it passes over the volume of water; and recovering a wet web of paper on the fabric suitable for pressing, drying and finishing to a sheet of paper.
• the above controlling may be automatic and include sensing the rise and fall of the pressure of the water in the box; and increasing and decreasing respectively the removal of water according to the sensed rise and fall of the pressure in the water volume in the box.
• the method preferably in ⁇ cludes removing water and entrained air from the dispersion and/or from the fabric followed by separating the air and the water so removed for separate treatment of each.
• the invention also includes a method of removing water from an aqueous fiber dispersion formed into a wet web including passing the fabric and wet web of fibers over and in contact with a submerged drainage removal means; applying a small vacuum to the removal means to extract water and air from the fabric and modifying con ⁇ sequently the natural tension of the meniscus of the water in the fabric to extract water from the wet fabric; and permitting air from the atmosphere to be applied to the removal means and thence to the fabric from below the
• SUBSTITUTESHEET fabric to enhance the removal of water from the fabric and water from the web.
• the air is introduced upstream from the vacuum whereby the air travels in the same direction as and in the interstices of the fabric and en ⁇ hances the removal of water from the web.
• Steam also may be applied to further enhance water removal from the web.
• This method may also include supplying another fabric on the wet web moving in the same direction as the fabric. The aforementioned steps of passing, applying, and permitt ⁇ ing are applied above the other fabric with the same effective results to produce a paper web and sheet there ⁇ from having substantially the same characteristics on each planar surface thereof.
• FIG. 1 is an overall schematic side elevational view of the system of this invention using two Fourdrinier fabrics
• FIG. 2 is a front elevational view of a drainage box in a Fourdrinier process modified in accordance with one embodiment of this invention
• FIG. 3 is a cross sectional view taken at 3—3 of FIG. 2;
• FIG. 4 is a front elevational view of a drainage box in a Fourdrinier process modified in accordance with a second embodiment of this invention, employing an automatic control;
• FIG. 5 is a cross sectional view taken at 5—5 of FIG. 4;
• FIG. 6 is a front elevational view of a drainage box in a Fourdrinier process including a means for removing entrained air in accordance with a third embodiment of this invention
• FIG. 7 is a cross-sectional view taken at 7—7 of FIG. 6;
• FIG. 8 is an enlarged cross-sectional view taken of a drainage box, similar to that taken at 8—8 of FIG. 4, but in considerably greater detail and with some modification thereto;
• FIG. 9 is a cross sectional view taken at 9—9 of FIG. 8;
• FIG. 10 is a cross sectional view taken at 10—10 of FIG. 8;
• FIG. 11 is a cross sectional view of the improved drainage box cover,taken transversely to the running blades, and usable on each of the drainage boxes illustrated in FIGS. 3, 5 and 7;
• FIG. 12 is an enlarged cross-sectional view of the drainage box taken at 12—12 of FIG. 1;
• FIG. 13 is an enlarged cross-sectional view of a portion of the drainage box of that shown in FIG. 12;
• FIG. 14 is identical to FIG. 13, except to include an improvement in the air inlet portion.
• the meniscus On the surface of the Fourdrinier fabric the meniscus infiltrates the interstices or meshes and produces several phenomena, one being that while a dry fabric is easily penetrated by air, the same fabric, when wet, will be difficult to penetrate by air and yet easily penetrated by the water. Since the film of the meniscus attaches to the fabric, it allows the passage of water, the meniscus itself being water. However, before air can pass through the fabric the meniscus layer must first be ruptured by a certain level of air pressure considered here as tension of the meniscus of water.
• a Fourdrinier paper making machine of the prior art is somewhat similar to the lower half of the apparatus of FIG. 1 wherein a woven fabric 20 travels horizontally in the direction of arrow 40 and passing over the top of several devices in locations such as those shown at 41, 42, 43, 32, 33, 34 and 35 to remove water from a layer of a fiber/aqueous dispersion 44 fed to the top of fabric 20 by a head box 115 and to leave a self supporting web of wet fiber at 109 which can be taken from the fabric 20 and processed through drying, pressing, and finishing operations to become a sheet of paper.
• the water removal devices of the prior art are normally boxes with a top cover of approximately 40-50% open area over which fabric 20 passes and with the interior of the box at subatmospheric pressure so as to suck water and/or air through the fabric 20 into the box for additional water removal.
• such boxes are fashioned with a plurality of parallel slots and/or holes and blades or foils, which are inclined against the direction of movement 40 of fabric 20 so as to cause water beneath the fabric to flow more readily through and away from the fabric 20.
• the purpose of such action is to essentially wipe away any bubble or any drops or hanging water below the bottom of fabric 20 and thereby seeking to maintain a flow of water draining out of the dispersion on the top of fabric 20 against the resistance formed by the meniscus of water attached along the interstices of the fabric.
• the guiding principle for the improved system of this invention is maintaining an uninterrupted continuous volume of water from fabric 20 to a place of
• This general system is now known as "submerged drainage” because the objective is to prevent any interfaces of water and air or other sur ⁇ faces which form a meniscus and which seriously impede the rapid drainage of water.
• the system must also provide means for destroying any meniscus as soon as it is formed so as to resume "submerged drainage”.
• FIGS. 2-3 show one system whereby the prior art ap ⁇ paratus is modified to employ components of this invention.
• the improved drainage box 52 having an internal volume 58 and a plurality of parallel blades 53 in an assembly frame 57, with an open area of at least about 90%, on top of the box is modified by the addition of- a bottom drainage means including drainage opening 110, a drainage tray 54, and a valve in ⁇ cluding a gate 55 pivoting about pin 56 to open or close drainage opening 110.
• a bottom drainage means including drainage opening 110, a drainage tray 54, and a valve in ⁇ cluding a gate 55 pivoting about pin 56 to open or close drainage opening 110.
• the valve remains closed.
• the internal space 58 is not filled with water.
• a vertical standpipe 61 is placed at the end of conduit 111 through flange connection 62 to receive the air and water passed thereinto.
• standpipe 61 At the upper end of standpipe 61 is a suction fan 59 blowing air outwardly in the direction of arrow 60 so as to create a vacuum in internal space 58.
• the lower portion of standpipe 61 serves as a hydraulic leg to seal the vacuum with water at level 66 draining through pipe 65 to a discharge below the water level 64 in a pond or col ⁇ lection vessel 63.
• This system of FIGS. 2-3 shows both the standpipe 61 and fan 59 as well as tray 54 and valve gate 55 which is not used to assist in providing a vacuum, via dif ⁇ ferential pressure action, on a volume of water in box 52 that extends in a continuous manner to the water in disper ⁇ sion 44 on fabric 20.
• FIGS. 4-5 One preferred embodiment, in accord with this inven ⁇ tion, is shown in FIGS. 4-5, and includes means to automati ⁇ cally control the water level in the drainage box 52 which in all respects are identical to that described above, as well as its internal space 58, blades 53, blade assembly frame 57, with an open area of at least about 90%, tray 54, valve gate 55, and pivot pin 56.
• an improved subassembly is attached to conduit 111 at flanges 62.
• a control tower 67 extends upwardly from conduit 111 and is filled with water to a level 71 which is slightly above the elevation of the inner or lower surface 38 of fabric 20.
• Above level 71 is a vacuum manifold 68 leading to a source of small vacuum, e.g., a fan, such as fan 59 in FIG. 2, with air flowing in the direction of arrow 69.
• a source of small vacuum e.g., a fan, such as fan 59 in FIG. 2
• cover plate 112 is provided as an access for cleaning conduit 111 and/or tower 67.
• the float 70 is designed to be maintained at level 71, but it will move up and down, and the movement of float 70 is sensed by transducer 102 to control via electric line 104 an electric motor and fluid pump 78 which pumps the fluid through fluid lines 79 and 80 to and from actuator 74 causing connecting rod 75 to move.
• the linear movement of rod 75 is transmitted through clevis 76 and arm 77 to cause shaft 72 to rotate about its longitudinal axis, which in turn, causes valve gate 55 to open or close.
• the level of water at lower surface 38 is controlled so as to maintain it at that elevation while sucking as much water as rapidly as possible away through box 52 and into tray 54 and out therefrom to pro ⁇ note a differential pressure effect, together with the modi ⁇ fication of the natural tension of the meniscus of water attached to the interstices of the fabric 20.
• FIGS. 6-7 Another embodiment of the invention is shown in FIGS. 6-7. Because of the imperfections involved in forming the
• SUBSTITUTESHEET fiber aqueous dispersion 44 placing it on fabric 20, and moving it through the process, there are pockets of entrained air found in dispersion 44 as it moves across drainage box 52.
• a means is provided to eliminate such for ⁇ mation and is seen to include a plurality of suction tubes 81 spaced apart from each other across the lateral width of fabric 20.
• tubes 81 are placed be ⁇ tween adjacent blades 53, preferably at least the most down ⁇ stream blades, and positioned at, or very near, to the bottom surface 38 of fabric 20.
• Tubes 81 are connected to a mani ⁇ fold 82 which leads to a source of low vacuum through conduit 68 in which air flows in the direction of arrow 69. Tubes 81 will cause water as well as air to pass from adjacent the bottom of the fabric 20 with the water being separated to flo downward in hydraulic leg 61 to a discharge level such as the level of water in tray 54.
• Control tower 67 is con ⁇ nected to internal space 58 in a drainage box 52 and is filled with water with a float 70 resting on the surface of the water and a vacuum line 68 leading off to a vacuum source (not shown), such as fan 59 of FIG. 2.
• a vacuum source not shown
• lever linkages 113 connected to float 70 by connector 116, cause shaft 88 to rotate in the direction of arrow 114.
• a valve plate 84 At the lower end of shaft 88 is a valve plate 84 with openings 86 extending ver ⁇ tically through plate 84.
• Valve seat 85 also has complementa openings 87 the iin, which generally match openings 86.
• the openings 86 and 87 will par ⁇ tially or fully align to permit water in tower 67 to flow int drop leg 61 and when fully unaligned will not permit water to so flow.
• Water in drop leg 61 fills up to a level at 66 and may be drained away in either of two ways; namely, through
• Valve 89 is a fine adjustment to divert the necessary water to side arm exit 90 and allow the remainder to fall into pond or vessel 63.
• Water from side arm exit 90 flows in the direction of arrow 91 into diaphragm valve 93 causing arm 96 to move up and down as the diaphragm 117 of valve 93 flexes.
• the dia ⁇ phragm guide is illustrated by numeral 118.
• Spring 97 is biased to hold levers 94 and 98 down until water in diaphragm valve 93 causes it to move upward.
• the covers 122 for the submerged drainage boxes 52 of FIGS. 2-7 are shown in FIG. 11 and are generally disclosed in the U.S. Patent Application Serial No. 07/326,384 filed March 21, 1989 corresponding to Italian Patent Application No. 83354/A/88, filed March 29, 1988 by Glauco Corbellini, and the subject matter thereof is incorporated herein by ref ⁇ erence.
• the submerged drainage box cover assembly 125 includes a lead blade 126 and trailing blade 127 which are preferably ceramic and fixed to respective rigid parallel bases 128 and 129 and assembled over lateral beams 130.
• a rigid box beam support or plate 131 joins the lateral beams 130 into a unitary assembly 125.
• the assembly 125 provides a series of blade holders 132 whereby individual ceramic de ⁇ flector blades 53 can be installed. Each blade 53 fits into a slot 133 and is glued together.
• the holder 132 is prefer ⁇ ably a laminated fiberglass unit constructed of multiple layers of fiberglass cloth bonded with epoxy resin.
• the bonding material 134 is preferably ceramic to metal and such material attaches lead blade 126 and trailing blade 127 to respective bases 128 and 129 and reinforced with screws.
• Box support plates 131 are connected to lateral beams 130 via a threaded key 135 located in keyway 136 and bolt 137.
• the holders 132 are affixed in the stainless steel members 138 by the key 124. As seen, the cover assembly 125 is supported on frame 139 forming the side walls of the suction boxes 52.
• the deflector mounting angle 140 preferably is between 35-60 degrees and this can be adjusted to obtain the desired drainage conditions for each of the drainage boxes 52.
• the contact nose surface 145 of each of blades 53 is normally between about 2-3 mm wide and gives an open area of about 90%.
• the divergence angle 146 is designed to be adjustable from about 5-15 degrees, depending on drainage conditions desired, even for the particular location of the drainage boxes 52 in the wetter end of the Fourdrinier.
• the blade holder slot thickness 141 can vary between about 3-4 mm and the blade spacing 142 can vary according to blade thickness 143, which is maintained between 6-9 mm, the desired open area and other physical dimensions of the assembly 125.
• the nose surface 145 of the blades 53, over which the fabric slides, includes an acute divergence angle 146, which has heretobefore not been disclosed in the above mentioned patent application nor the above open area or other preferred dimen ⁇ sions for the particular purposes of the herein disclosed system, and these are important in submerge, drainage to min ⁇ imize the contact with the fabric and to cause more water to be drained from the fabric as it is passing over the blades 53 offering an open area of at least about 90% with a de ⁇ flector angle 140 of approximately 45°.
• FIGS. 12-14 show an improved design for a drainage box for the drier end of the Fourdrinier machine to be used in place of the high vacuum flat suction boxes of the prior art, and FIG. 1 shows a preferred arrangement for their use.
• FIG. 1 shows a preferred arrangement for their use.
• the lower part of FIG. 1 is somewhat similar in many respects to the prior art Fourdrinier paper making
• FIG. 1 has combined an auxiliary Fourdrinier system in the drier end of the drainage area, which is somewhat generally known in the prior art, as shown for example, by U.S. Patent No. 4,306,934, dated December 22, 1981 invented by Erkki 0. Seppanen.
• An upper Fourdrinier fabric 21 has an outer surface 31 in contact with the upper surface of the web 44', which has now formed by the prior dewatering operation acting on aqueous dispersion 44, so as to have fabric 20 below the web 44' and fabric 21 above the web 44'.
• Both fabrics 20 and 21 are horizontal with the dis ⁇ persion 44 and web 44' supported on lower fabric 20 and both fabrics 20 and 21 are made to run in the same direction 40 where they are closely parallel to each other. Since each fabric 20 and 21 is separate and distinct and is an endless length, they must each be driven, guided, and tensioned by separate sets of rollers.
• FIGS. 12-14 Both upper and lower submerged drainage boxes are made of a plurality of drainage cells 121 as shown in FIGS. 12-14.
• Each cell is constructed generally as shown in FIG. 13 having a central vacuum chamber 50 maintained at subatmospheric pressure, a nose 51 in sliding contact with the inside sur ⁇ face (38 of fabric 20 or 30 of fabric 21) with inclined passageways 48 and 49 leading toward and away from nose 51.
• Three such cells are shown in FIG. 12 extending laterally across fabrics 20 and 21 in generally the same fashion as blades 53 in FIGS. 2-7, and 11.
• One end of each vacuum chamber 50 is opened into an individual conduit like conduit 111 of FIG.
• conduit 111 a conduit, like conduit 111, where the air and water is separated by reason of water falling into the water in standpipe 61 and being drained away into pond or vessel 63 while the air is blown away, through fan 59.
• the other end of vacuum chamber 50 is closed so as to force all air and water into conduit 111.
• air and water is sucked through pas ⁇ sageway 49 into chamber 50, air from the surrounding atmo ⁇ sphere flows into passageway 48 to pass over nose 51 and through the fabric 20 below or the fabric 21 above.
• the combination of three rows of cells as shown in FIG. 12 includes a lead deflector surface 45, intermediate deflectors 46, and trailing deflector surface 47, all being stationary surfaces over which the moving fabric 20 or fabric 21 travels. Such surfaces are needed to support the fabric 20 and 21 in a smooth stable manner.
• a pipe 105 carrying steam to spray downwardly out at 106 into passageway 48 enhances the operation by heating the air passing through passageway 48 and thereby heating the water in web 44 causing its viscosity to be lowered and thereby making it flow more rapidly through fabric 20 or 21.
• An in ⁇ sulated reflector 108 is shown to protect against loss of the heat before it is sprayed at 106. The entrance of air into passageway 48 is permitted by opening 107 through reflector 108.
• the upper drainage boxes or cells are horizontally offset from the lower drainage boxes so that a vacuum is not applied to each side of the paper web at the same time at a particular location. If this were not so, it is likely that air may occasionally pass through and damage the paper web. Also, the spacing or tolerance between the upper and lower fabrics might cause damage thereto on account of entrained debris in the web and to inhibit such damage the water is not withdrawn from the web simultaneously vertically at any particular location spaced along the two fabrics.

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• Paper (AREA)
• Insulation, Fastening Of Motor, Generator Windings (AREA)
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• 1990
  • 1990-07-23 AT AT90911884T patent/ATE130891T1/de not_active IP Right Cessation
  • 1990-07-23 ES ES90911884T patent/ES2081999T3/es not_active Expired - Lifetime
  • 1990-07-23 EP EP90911884A patent/EP0439571B1/de not_active Expired - Lifetime
  • 1990-07-23 DE DE69023894T patent/DE69023894T2/de not_active Expired - Fee Related
  • 1990-07-23 WO PCT/US1990/004144 patent/WO1991001408A1/en active IP Right Grant
  • 1990-07-23 CA CA002040439A patent/CA2040439C/en not_active Expired - Fee Related
• 1991
  • 1991-04-22 FI FI911934A patent/FI911934A0/fi unknown

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