Abstract:
A microvalve assembly ( 10 ) includes an elongate valve body ( 14 ) having opposed first and second major surfaces, the first major surface defining a valve recess ( 34 ) and the second major surface defining first and second fluid ports ( 20,22 ). Both the fluid input port and the fluid output port extend in fluid communication with the valve recess. A gasket ( 12 ) is freely positioned within the valve recess so as to extend in overlying registry with either or both of fluid ports. A valve cover ( 16 ) is bonded to the valve body and includes a first planar surface positioned in overlying registry with the valve recess so as to enclose the gasket therein. The valve cover is deflectable into the valve recess so as to cause the gasket to seal at least one of the fluid ports.

Description:
This application is a filing under 35 U.S.C. 371 of international application number PCT/US2010/062453, filed Dec. 30, 2011, which claims priority to U.S. application No. 61/291,464 filed Dec. 31, 2009, the entire disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to the field of microfluidics. More specifically, the present invention is directed to a microfluidic valve. 
     BACKGROUND OF THE INVENTION 
     There are many variations of membrane valves. Classical microfluidic membrane valves use either a hard-hard seal with very smooth micromachined surfaces, or incorporate a complete additional layer of a soft material between two hard layers. In all cases a good valve seal under practical situations relies on a hard material in contact with a soft material, or a soft material in contact with a soft material. Microfluidic devices are fabricated from polymers for high volume manufacturing, utilize injection moldable materials, and offer the advantage of high levels of integration. One challenge resulting from microfluidic devices fabricated in this way is that the devices are constructed from layers that are finally bonded together. The choice of materials is limited by both the final intended application and available manufacturing techniques. Examples of factors to consider are the application process chemicals and temperatures, and the fabrication processes such as molding and bonding. Satisfying the material requirements of a membrane valve at the same time as all other components that are intended to be part of the monolithic final device, without working with dissimilar materials that are difficult to join, can result in a valve that has a hard membrane pressing against a hard substrate. 
     The work of Jerman (“Electrically-activated, normally-closed diaphragm valves”, J. Micromachining and Micrengineering, V4, 1994 pp 210-216), describes a silicon-on-silicon micromachined valve. Smooth surfaces resulted in leakage rates (on:off flow rates) of 5000:1. 
     The work of Bruns (Silicon Micromachining and High-speed gas chromatography, Proceedings of the 1992 International Conference on Industrial Electronics, Control, Instrumentation and Automation, 1992, V3, pp 1640-1644) describes a trapped polymer membrane between a glass membrane and a silicon valve body, to replace the hard-hard valve seal with a hard-soft valve seal. 
     The recent work of Chen et al (Floating-Disk Parylene Microvalves for Self-Pressure-Regulating Flow Controls, Journal Of Microelectromechanical Systems, Vol. 17, No. 6, December 2008), describes a silicon and parylene valve structure that consists of a floating parylene disc. The work in the paper aims to produce a passive valve with self-regulating behavior resulting from the movement of the floating parylene disc. 
     There is thus a need for a microvalve having a simple design which provides ease of manufacture and satisfactory performance. More specifically, there is therefore a need for a microvalve formed from bonding similar materials together for the fabrication of the microvalve, while simultaneously introducing a soft layer for valve sealing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a microvalve of the instant invention. 
         FIG. 2  depicts a cross-sectional view of the microvalve of  FIG. 1 , taken through the line  2 - 2 . 
         FIG. 3  depicts an exploded view of a microvalve of the present invention. 
         FIG. 4  depicts a cross-sectional view of the microvalve of  FIG. 2  in a closed position by action of an external actuator which deflects the valve cover so as to pin the floating gasket in sealing engagement over the valve output port. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention describes the assembly of a soft material disc into a valve that otherwise consists of hard-on-hard materials. Without introducing an additional soft material into a hard-hard system, it is difficult to form a good valve seal without applying extremely high forces which jeopardize the reliability of the valve. 
     One alternative to assembling a floating disc is to bond the disc to the valve membrane. The complications in bonding the membrane are that the adhesive used for bonding or the choice of materials that are capable of being joined without adhesives, must be compatible with the application process. Early work on the membrane valve showed that a soft polypropylene (PP) layer 20 μm thick, bonded to a COC film 190 μm thick, produced a good seal to a PEEK valve body. The configuration was capable of sealing gas or water up to 6 bar gage pressure with a force less than 20 Newton applied to a valve seat approximately 1 mm in diameter and 40-100 μm wide. Unfortunately the PP layer bonded to the COC film prevented the COC film from bonding to a COC valve body without the use of an adhesive. Furthermore, removal of the PP from the COC film in all areas except the valve seat or alternatively the entire valve, exposed the COC-PP bonding adhesive on the edge to the fluid being directed through the valve, leading to potential chemical attack of the adhesive. Attempts to form an equivalent valve from a COC film without the bonded PP layer showed that the COC membrane could be successfully bonded to the COC valve body without an adhesive, however the resulting valve consistently suffered from leakage. 
     Another option is to use 2 K (two compound) molding to fabricate the valve body, where the valve seat is produced from a soft material. While satisfying the criteria for a good valve seal, this path is more costly and again restrictive in the choice of materials. 
     The present invention describes a solution for designing and producing a structure consisting of layers that can be bonded together, and may consist of hard-hard material combinations, while still satisfying the condition of a hard-soft material combination for valve sealing. This freedom in the valve design leads to many technical and commercial advantages. Technically, it provides a new degree of freedom in selecting the appropriate materials for the overall device, such as thermal performance or chemical stability, independently and free from concerns of satisfying the hard-soft requirement for a good valve seal. Commercially, the degree of freedom allows the device to be produced from layers of similar, or even the same material, reducing the complexity and cost of manufacturing. It also allows the same design to be produced in different families of materials for different applications, without the need for lengthy solutions to completely redesign the valve. 
     The invention works by inserting a thin disc of a soft gasket material between a valve body and a valve membrane, or valve cover, prior to bonding the valve membrane to the valve body. The thin disc could be of a material such as Teflon. A thickness in the range of 5 μm to 1 mm is possible since the thin disc is not bonded to the valve membrane and for this reason it does not affect the force-deflection performance of the valve membrane. 
     With reference to  FIGS. 1-4 , the present invention provides a microvalve  10 . Microvalve  10  includes a soft floating gasket  12 , assembled between a valve body, or substrate,  14  and a deformable membrane, or cover,  16 , prior to bonding of membrane  16  to valve body  14 . Valve body  14  and valve cover  16  may be formed, for purposes of illustration and not of limitation, from COC (cyclic olefin copolymer). Floating gasket  12  is made from a soft material, such as Teflon®, that eliminates the hard-on-hard surface when the valve is in a ‘closed’ configuration and relaxes the constraints on the selection of fabrication materials. Valve body  14  and cover  16  define a valve recess  18  therebetween, in which gasket  12  is positioned. Additionally, valve body  14  defines a first fluid port  20  and a second fluid port  22 , both ports  20  and  22  in fluid communication with valve recess  18 . Valve body  14  defines an inlet aperture  24  and an elongate inlet passage  26  extending in open fluid communication between first port  20  and inlet aperture  24 . Valve body  14  further defines an outlet aperture  28  and an elongate outlet passage  30  extending in open fluid communication between second port  22  and outlet aperture  28 . Valve  10  may thus be connected to two fluidically-isolated fluid conduits (or channels) at apertures  24  and  28  to regulate the flow therethrough. 
     Valve body  14  desirably includes a planar major surface  32  which defines a recess aperture  34  over which cover  16  spans so as to define valve recess  18  between valve body  14  and cover  16 . Valve body  14  desirably includes an annular rim  36  recessed from major surface  32  and extending between co-axial cylindrical surfaces  38  and  40 . Gasket  12  desirably is in the shape of a circular disc that that is at least partially co-extensive with annular rim  36  so that gasket  12  is perimetrically bounded between cover  16  and annular rim  36 . The present invention further contemplates that gasket  12  is sized to span across valve recess  18  such that it also extends at least half or more of the width of rim  36  (that is, the perimetrical edge of gasket  12  desirably extends half-way or more between surfaces  38  and  40 ). Further still, the present invention contemplates that gasket  12  is sized and shaped to substantially span across recess aperture  34  so as to be substantially co-extensive with rim  36 . 
     Valve body  14  further includes a substantially planar annular floor surface  42  in facing opposition to cover  16 . Floor surface  42  defines first port  20 . Valve body  14  further includes a valve seat  44  which defines second port  22  and assists in seating the foil gasket. Valve seat  44  extends further into valve recess  18  (i.e, closer to cover  16 ) than floor surface  42 . Valve seat  44  includes a first portion  46  immediately about second port  22  and a second portion  48  sloping towards floor surface  42  so as to be non-transversely-oriented with the longitudinal axis of second port  22 . Valve port  22  is desirably co-axially aligned with valve recess  18  so as to be centrally located under cover  16 , thus the portion of cover  16  which is maximally deflected will press gasket  12  against valve seat  44  and thus fluidically isolate fluid port  22  when valve  10  is in a ‘closed’ orientation. 
     Arrows A and B in  FIG. 2  depict the deflection of the valve cover  16  and gasket  12  both towards and away from a position where gasket  12  is in sealing registry with second fluid port  22 . When the gasket is in the undeflected position, first fluid port  20  is in fluid communication with second fluid port  22 , allowing a fluid flow therebetween through valve  10 . When gasket  12  is in the deflected position, the gasket seals second fluid port  22  from first fluid port  20  and prevents flow therebetween through valve  10 . The choice and dimension of the material used for valve cover  16  may be dictated by the dimensions of valve  10 . The material used will allow gasket  12  to be deflected in accordance with the present invention. 
     As shown, gasket  12  sits in recess  18 . Gasket  12  may be floating, however the present invention desirably provides gasket  12  loosely pinned in place between rim  36  and cover  16  as 1) it spans the valve recess and 2) it is pressed against the annular shelf of the valve body by COC membrane  16  at its perimeter. For these reasons gasket  12  offers the advantages of being attached to valve membrane  16 , being positioned precisely over valve seat  44 , not introducing significant additional dead volume in recess  18 , and not affecting the elastic deformation behavior of valve membrane  16 . 
     Additionally, annular valve seat  44  is desirably formed as a sloping surface extending up to second fluid port  22 . The sloping surface rises from first fluid port  20  which opens adjacent to second fluid port  22 . Desirably, both fluid ports  20  and  22  open in facing opposition to gasket  12 , however the present invention contemplates that first fluid port  20  may be located anywhere which will be in fluid communication with the second fluid port when gasket  12  is undeflected (i.e, spaced from valve seat  44 ). 
     As seen in  FIG. 4 , valve  10  can be operated by a mechanical plunger  50  that presses the membrane  16  towards, and gasket  12  against, valve seat  44 . Alternatively, valve cover  16  may be deflected to press gasket  12  onto valve seat  44  by directly applying pressure to the membrane  16  opposite valve recess  18 . The present invention contemplates that the direct pressure can be applied through a manifold that is pressed against the top of valve cover  16 , where individual manifold chambers apply pressure to an associated microvalve  10  that need to be controlled independently. External actuation of valve membrane  16  allows a simpler and lower cost valve, even allowing the valve to be disposable. 
     While a particular embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the teaching of the instant invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.