Filter unit with thermoplastic overmold seal member

Abstract
The present invention provides a filter cartridge or filter unit (11) produced by a thermoplastic overmolding process that allows for using a single mold for overmolding a variety of different sized filter elements (12) or membranes and a method for sealing or hermetically sealing said filter element (12) in said filter unit (11) or cartridge. The proposed method produces a more robust filter unit (11) or cartridge than those provided by the prior art.
Description




This invention relates to a method for sealing a filter element in a filter cartridge and filter devices produced therefrom.




Filter cartridges are used with a variety of types of filtration media, typically membranes for sterile filtration and sample preparation. The present invention provides an improved method for sealing a filter element in a filter cartridge by overmolding. The present method for overmolding filter cartridges results in a less expensive and improved filter cartridge.




One problem is that currently, a different sized filter cartridge overmold is needed for each different size of filter disk. Needing an overmold for each size of filter disk, in addition to the molds needed to create the two support halves of the filter cartridge, is expensive. Such overmolds are necessary because in the prior art devices the outer edge of the filter housing, the two support pieces being coupled with an overmold, is used to secure the outer edge of the filter sheet to prevent leakage. Indeed, it follows that the prior art filter housing circumference had to be substantially equivalent to the circumference of the filter sheet or media.




For instance, U.S. Pat. No. 4,113,627 discloses a method for hermetically sealing a membrane in filter devices, e. g. filter cartridges. Specifically, it discloses a method comprising the steps of molding a thermoplastic filter support element which has the filtrate passing aperture formed therein, aligning the filter element over the aperture and the adjacent surface portions of the support, applying pressure to the filter element and the adjacent surface portions of the support to capture the edge of the filter element against the support and to form the integral seal between the support and the filter element.




In addition to the above mentioned problem, prior art filter cartridges may burst when subjected to significant pressure. Such bursting may be due to the failure to properly secure the support portions to each other. Such bursting may also be a result of the limitations of the prior art design of such filter cartridges.




The method of the present invention allows for a single overmold to be used to manufacture filter cartridges that can contain different diameters of filter disks. The present invention also provides an overmolding method that produces a complete filter cartridge that is less likely to burst under conditions that would make a prior art device burst.




The present invention provides a method for sealing a filter element in a filter cartridge or filter unit, comprising the steps of:




molding a thermoplastic support or housing in two parts, one first support part and one second support part for the filter element, each support part having at least one fluid flow passageway and said first support part having formed therein at least one overmold flow passageway,




aligning the filter element between the first support part and the second support part of the thermoplastic support or housing so that the filter element covers the fluid flow passageway(s) and so that its periphery is adjacent to the overmold flow passageway(s) and adjacent to the surface portions of the two support parts of the support or housing,




holding the filter element in position on the support or housing and,




injection molding a compatible thermoplastic material that flows over at least a portion of the periphery of the filter element and through the overmold flow passageway(s) such that an integral sealing member between the two support parts of the support or housing and the filter element is formed.




The present invention also provides a method for hermetically sealing a filter element, the method comprising the steps of:




molding a thermoplastic support or housing for the filter element between two mold halves, said thermoplastic support or housing being realized as first and second support parts which respectively have at least one opening inlet and one opening outlet for the passage of a fluid and said support or housing having at least one aperture For the passage of an overmold material,




removing one of the mold halves to expose the surface of the first support part on which the filter element is to be located,




aligning the filter element so that it covers the at least one opening inlet and one opening outlet for the passage of a fluid, so that the filter element is adjacent to the surface portions of the first support part and the filter element's periphery is adjacent to the at least one overmold flow passageway,




placing a new mold half containing the second support part over said first support part, the filter element and the remaining original mold half, the new mold half having portions which contact and apply pressure to the filter element near the edge of the overmold flow passageway(s), the new mold half and the second support part forming a channel along the periphery of the filter element and a portion of the internal surface of the first support part in the first mold half,




injection molding a compatible thermoplastic material into the channel that flows along the periphery of the filter element and against the internal surface of the first support part and through at the least one overmold aperture to the second support part to form an integral sealing member between the said two support parts, the filter element and the compatible thermoplastic material, and




separating the mold halves and ejecting the complete support or housing and its integral filter element.




The present invention further provides a filter unit for removing contaminants from a fluid stream, comprising:




a thermoplastic support member or housing, a porous filter element and a thermoplastic overmold sealing member,




said thermoplastic support member or housing being formed of a first support part and a second support part, each having at least one fluid flow passageway, and at least one thermoplastic overmold passageway,




said filter element extending over said fluid flow passageway(s), its periphery adjacent to at least one thermoplastic overmold passageway and secured to said thermoplastic first and second support parts by said thermoplastic overmold scaling member also being disposed through the thermoplastic overmold passageway(s).




It is an object of the present invention to allow different diameter membranes to be molded into filter unit or cartridges using the same tool.




It is another object of the present invention to reduce the dead volume of filter unit (filter cartridges).




It is another object of the present invention to produce a filter unit or cartridge that can withstand higher pressures than those currently available.




It is another object of the present invention to maintain the integrity of membranes (filter elements) used in filter units or cartridges by sealing them with a thermoplastic overmold rather than being pinched by a filter support or supports.




It is another object of the present invention to provide thermoplastic overmold passageways that allow the thermoplastic overmold material to flow over the periphery of the membrane and onto the support to provide improved pressure performance.




It is another object of the present invention to provide a membrane support design that assists in avoiding membrane obturation when a soft male luer part is connected to the cartridge or filter unit inlet.




It is another object of the present invention to have superior housing capability by reducing the flexion in comparison with the prior art.




It is another object of the present invention to reduce the cost of manufacturing as well as the time needed to manufacture.











The above gives a broad description of the present invention one preferred form of which will now be described with reference to the accompanying drawings in which:





FIG. 1

is a cross section of a prior art filter unit or filter cartridge;





FIGS. 2



a


and


2




b


illustrates two rough cross-sectional views of comparing the present invention (


2




a


) with the prior art (


2




b


);





FIGS. 3



a


and


3




b


illustrates two cross-sectional views of filter assemblies according to the present invention where filter elements or membranes having different diameters are used;





FIG. 4

illustrates an exploded view of a filter assembly according to the present invention; and





FIG. 5

illustrates the overmolding operation in the method of the present invention.












FIG. 1

shows a cross-section of a prior art filter unit


1


. This filter unit


1


includes a filter element


2


disposed internally of a housing


3


with inlet and outlet openings


5


and


7


on two parts


4


and


6


, respectively. These parts are assembled and fused or bonded into an integral filter unit


1


by means of an injection molded sealing member


8


of thermoplastic material. Sealing member


8


completely surrounds and fills joint


9


and thereby forms an integral part of the filter unit


1


. In the represented embodiment one of the housing parts has a shortened exterior lip


10


such that at least a part of the lateral surface of filter element


2


will be directly exposed to the thermoplastic sealing member


8


.





FIG. 2

illustrates the structural differences between the filter assembly (filter unit


11


) according to the present invention (a) and the filter device


1


according to the prior art (b).




As seen on

FIGS. 3

,


4


and


5


, the filter unit


11


according to present invention includes a filter element


12


disposed internally of a housing


13


with inlet and outlet openings


15


and


17


on a first support part


14


and a second support part


16


, respectively. As shown on theses figures, the cross section of the inlet and outlet openings


15


and


17


on the first support part


14


and the second support part


16


are much smaller in comparison to the cross section of the filter element


12


thereby giving the filter unit


1


a characteristic shape. The support parts


14


,


16


are assembled and fused or bonded into the integral filter unit


11


by means of an injection molded sealing member


18


of thermoplastic material.




As shown in detail on

FIG. 2



a


, first support part


14


and second support part


16


form a housing


13


in a sandwich-like shape around the filter element


12


. Both portions of said first and second support parts


14


and


16


are overmolded with an thermoplastic overmolding material to form a sealing member


18


, which is very different to the prior art represented on

FIG. 2



b


where the sealing member


8


merely joins the periphery of supports


10


and


12


. In case of high pressure fluid flows applied to such a filter unit


1


, the hazard of the sealing member


8


which acts like a clamp to be blasted off the supports


10


and


12


is not neglectible. This makes the prior art devices quite unreliable for high performance appliances where high pressure and flow rates are applied to the filter units


1


.




In addition, this

FIG. 2



b


clearly demonstrates that the filter


2


of the prior art device (filter unit


1


) must have a diameter substantially similar to that of the parts


4


and


6


. As

FIG. 2



a


provides, in the present invention the diameter of the filter element


12


or membrane is independent of the diameter of first and second support parts


14


and


16


. This is due to the overlap


19


of thermoplastic overmold that secures the filter element


12


. This overlap


19


occurs because the first support part


14


has an overmold flow passageway


20


designed as a channel that allows the thermoplastic overmold material to flow between the first and second support parts


14


and


16


over the filter element


12


to form an overlap


19


of overmold thermoplastic. The overmold thermoplastic then flows through at least one aperture


21


in the first support part


14


into an annular groove


22


such that pool


23


′ of overmold thermoplastic forms on the back side of the first support part


14


(

FIGS. 3



a


and


3




b


). Upon solidifying, the aperture(s)


21


is (are) filled to form one or more rivets


23


and provide(s), along with the pool


23


′ of overmold thermoplastic, preferably in a circular shape, additional strength to the filter unit


11


(

FIGS. 3



a, b


and


4


). This construction allows the filter unit


11


or cartridge of the present invention to have a significantly higher burst pressure than those of the prior art.





FIG. 3

illustrates a comparison of the present invention where the filter element


12


has different diameters X or Y. The comparison demonstrates that the diameter of the first and second support parts


14


and


16


are independent of the diameter of the filter element


12


. This means that only a single mold is needed for the overmolding process.

FIG. 3

is also a sectional view of two embodiments of the present invention. Both recite the use of a fluid inlet aperture


15


and outlet aperture


17


to form a fluid flow passageway. They also recite the use of an anti-obturation plate


24


. This structure of the anti-obturation plate


24


which is also partly shown on

FIG. 4

allows the flow of fluid to be filtered by the filter element


12


but prevents a male luer fitting from pressing against the filter element


12


. If this were to occur, a substantial portion of said filter element


12


would be blocked and could not be used.





FIG. 4

provides an exploded view of a filter unit


11


(filter cartridge) of the present invention. The supports


14


and


16


sandwich the filter element


12


(also referred to as the membrane), the <<sandwich >> being held together by the thermoplastic overmold (sealing member


18


). One particular aspect of the present invention illustrated by this figure is the rivet(s)


23


that reside(s) in the hole(s)


21


in the first support part


14


.




Since the rivet(s)


23


is/are backed by the thermoplastic overmold, which has in this case a shape of a ring, the filter unit


11


or cartridge has substantially improved burst characteristics as compared with prior art devices.





FIG. 4

also provides another aspect of the present invention by the means of a centering aid


25


that facilitates the use of the filter unit


11


in automated sample preparation processes. Indeed, as the present invention has de-coupled the need for circular supports, the present invention could utilize circular filter elements


12


or membranes sandwiched between polygonal-shaped or more unconventionally-shaped first and second support parts


14


,


16


.




Polygonal first and second supports part


14


,


16


and therefore filter units


11


or cartridges would be preferable as they are more easily handed by the various robotic automation systems that are in current favor. Polygonal filter units


11


, i. e. square section shaped filter units may also be less bulky and thus easier and cheaper to store.




The present invention provides a method for sealing a filter element


12


in a filter unit


11


or cartridge comprising the steps of:




molding a thermoplastic support or housing


13


in two parts, a first support part


14


and a second support part


16


for the filter element


12


, each support part


14


,


16


having at least one fluid flow passageway and said first support part


14


having formed therein at least one overmold flow passageway


20


,




aligning the filter element


12


between the first support part


14


and second support part


16


of the thermoplastic support or housing


13


so that the filter element


12


covers the fluid flow passageway(s) and so that its periphery is adjacent to the overmold flow passageway(s)


20


and adjacent to the surface portions of the two support parts


14


,


16


of the support or housing


13


,




holding the filter element


12


in position on the support or housing


13


and,




injection molding a compatible thermoplastic material that flows over at least a portion of the periphery of the filter element


12


and through the overmold flow passageway(s)


20


such that an integral sealing member


18


between the two support parts


14


,


16


of the support or housing


13


and the filter element


12


is formed.




The method of the present invention is characterized in that the peripherical surfaces of the first support part


14


and the second support part


16


adjacent the overmold flow passageway(s)


20


are shaped so that they may receive the thermoplastic material used in the overmolding step.




In one first embodiment the peripherical surfaces of the first


14


and second


16


support parts adjacent the overmold flow passageway(s)


20


are furrow-shaped to receive the thermoplastic material used in the overmolding step.




In a second embodiment (non represented) one of the support parts


14


,


16


is cup-shaped whereas the other corresponding support part


14


,


16


is realized as a cover resting on said cup, the peripherical surfaces adjacent the overmold flow passageway(s)


20


being assembled by the thermoplastic material used in the overmolding step. The two support parts


14


,


16


forming the covered cup shaped housing


13


may also be provided with supplementary bonding means in order to be assembled together before the thermoplastic material is injected in the formed housing


13


during the overmolding step.




For example, the two first


14


and second


16


support parts forming the covered cup may be screwed, glued or welted together before the thermoplastic material is injected in the formed housing


13


through the existing overmold flow passageway(s)


20


during the overmolding step.




According to another embodiment the present invention provides a method for hermetically sealing a filter element


12


, the method comprising the steps of:




molding a thermoplastic support or housing


13


for the filter element


12


between two mold halves, said thermoplastic support or housing


13


being realized as first


14


and second


16


support parts which respectively have at least one opening inlet


15


and one opening outlet


17


for the passage of a fluid and said support or housing


13


having at least one aperture


21


for the passage of an overmold material,




removing one of the mold halves to expose the surface of the first support part


14


on which the filter element


12


is to be located,




aligning the filter element


12


so that it covers the at least one opening inlet


15


and one opening outlet


17


for the passage of a fluid, so that the filter element


12


is adjacent to the surface portions of the first support part


14


and the filter element's


12


periphery is adjacent to the at least one overmold flow passageway


20


,




placing a new mold half containing the second support part


16


over said first support part


14


, the filter element


12


and the remaining original mold half, the new mold half having portions which contact and apply pressure to the filter element


12


near the edge of the overmold flow passageway(s)


20


, the new mold half and the second support part


16


forming a channel


20


along the periphery of the filter element


12


and a portion of the internal surface of the first support part


14


in the first mold half,




injection molding a compatible thermoplastic material into the channel


20


that flows along the periphery of the filter element


12


and against the internal surface of the first support part


14


and through the at least one overmold aperture


21


to the second support part


16


to form an integral sealing member


18


between the said two support parts


14


and


16


, the filter element


12


and the compatible thermoplastic material, and




separating the mold halves and ejecting the complete support or housing


13


and its integral filter element


12


.




The present invention provides a filter unit


11


for removing contaminants from a fluid stream, comprising:




a thermoplastic support member or housing


13


, a porous filter element


12


and a thermoplastic overmold sealing member


18


,




said thermoplastic support member or housing


13


being formed of a first support part


14


and a second support part


16


, each having at least one fluid flow passageway, and at least one thermoplastic overmold flow passageway


20


,




said filter element


12


extending over said fluid flow passageway(s), its periphery adjacent to at least one thermoplastic overmold flow passageway


20


and secured to said thermoplastic first and second support parts


14


,


16


by said thermoplastic overmold sealing member


18


also being disposed through the thermoplastic overmold flow passageway(s)


20


.




In a special embodiment the filter unit


11


of the present invention further comprises means for minimizing obturation of the filter element


12


by male luer fittings, for example an anti-obturation plate


24


.




In another special embodiment the filter unit


11


of the present invention further comprises means for centering said filter unit


11


when used in automated applications, for example a centering aid


25


.





FIG. 5

is a graphic presentation of a filter unit


11


of the present invention as thermoplastic overmold material is injection-molded into two first and second support parts


14


and


16


forming the housing


13


of said filter unit


11


while residing in a mold


26


. The filter element


12


or membrane is pinched between the first and second support parts


14


and


16


for a tight contact


27


and then the hot thermoplastic overmold material


28


is injected from injection gate


29


. One or both of the housing


13


may also include a plurality of concentric ribs or rib-pieces


30


which are disposed inwardly of the outer portion of support parts


14


and


16


to provide an improved drain design for enhanced liquid repartition.




In an preferred embodiment, the thermoplastic overmold has a special color to indicate which type of filter is embedded in the manufactured filter unit


11


, since the filter unit


11


cannot be dismantled once it has been formed and cooled.




The thermoplastic material used for the overmolding in the present invention and the operating conditions used for the overmolding process are those common to those skilled in the art. The thermoplastic material may, for example, be chosen from a wide range of plastics which are well known in the art, such as cellulose propionate, nylon, polyester, polypropylene, ABS, polyethylene, and vinyl among others.




Concerning the particular parameters and processing procedures utilized in the injection molding process, these may vary depending on the material and equipment and are also well known in the art. As a non-restrictive example where the housing


13


and sealing member


18


are composed of an ABS thermoplastic resin, a suitable injection temperature will be in the range of about 230° C. and the injection pressure will be approximately 10


7


Pa.




Described herein above is a method or process for producing a filter unit


11


or cartridge, said method or process resulting in the decoupling of the shape and size of the filter element


12


or membrane with the shape and size of the two support parts


14


and


16


forming the housing


13


in which it is to be overmolded.




The process also produces a filter unit


11


or cartridge having superior bursting characteristics. In this disclosure, there is shown and described only the preferred embodiment of the invention. However, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the invention concept as expressed herein.



Claims
  • 1. Filter unit for removing contaminants from a fluid stream, comprising:a thermoplastic support member or housing, a porous filter element and a thermoplastic overmold sealing member, said thermoplastic support member or housing being formed of a first support part and a second support part, each having at least one fluid flow passageway, and at least one thermoplastic overmold flow passageway, at least one aperture formed in one of said first and second support parts at an inner end of the at least one thermoplastic overmold flow passageway, said filter element extending over said at least one fluid flow passageway, its periphery adjacent to at least one thermoplastic overmold flow passageway and secured to said thermoplastic first and second support parts by said thermoplastic overmold sealing member also being disposed through the at least one thermoplastic overmold flow passageway and the thermoplastic overmold sealing member also being disposed in the aperture.
  • 2. Filter unit for removing contaminants from a fluid stream, comprising:a thermoplastic support member or housing, a porous filter element and a thermoplastic overmold sealing member, said thermoplastic support member or housing being formed of a first support part and a second support part, each having at least one fluid flow passageway, and at least one thermoplastic overmold flow passageway, at least one aperture formed in one of said first and second support parts at an inner end of the at least one thermoplastic overmold flow passageway, said filter element extending over said at least one fluid flow passageway, its periphery adjacent to at least one thermoplastic overmold flow passageway and secured to said thermoplastic first and second support parts by said thermoplastic overmold sealing member also being disposed through the at least one thermoplastic overmold flow passageway and the thermoplastic overmold sealing member also being disposed in the aperture in the form of a rivet.
Parent Case Info

This application is a divisional of application Ser. No. 09/650,372, filed Aug. 28, 2000 now U.S. Pat. No. 6,403,008.

US Referenced Citations (7)
Number Name Date Kind
4113627 Leason Sep 1978 A
4874513 Chakraborty et al. Oct 1989 A
5230727 Pound et al. Jul 1993 A
5556541 Ruschke Sep 1996 A
5688460 Ruschke Nov 1997 A
6033455 Kurashima Mar 2000 A
6274055 Zuk, Jr. Aug 2001 B1