Abstract:
A method of forming a fiber or continuous filament from two fiber components which includes the steps of positioning a first plate having first openings adjacent a second plate having second openings, positioning flexible tube members to be in communication with the first openings and to extend into the second openings, causing the flexible tube members to flex to accommodate any axial misalignment between the first and second openings, and creating flow paths of first and second fiber components to form the fiber or continuous filament.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 09/191,663, filed Nov. 13, 1998, now U.S. Pat. No. 6,168,409, issued Jan. 2, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to an apparatus and method for the formation of a fiber or continuous filament, and more particularly to the formation of a fiber which consist of two separate and different components. 
     It is well known to form synthetic fibers by extruding molten polymers through a large number of very small openings formed in a die. 
     It is also well known that such synthetic fibers can be formed of two polymer components having different characteristics and physical properties, such as so-called “sheath-core” fibers that have one component (the core) centered within the other (the sheath). In forming these sheath-core fibers, it is very important that the core be centered within the sheath because if the core is offset from the center by even a slight amount, the quality and physical properties of the resulting fiber can be seriously flawed. 
     In forming these sheath-core fibers, it is common practice to provide a pre-die plate which is formed with a first plurality of openings extending therethrough and through which one of the components flow, and a second die plate having a second plurality of openings through which the second component flows as it becomes joined with the first component and is discharged through the bottom or discharge openings in the die plate in the aforesaid sheath-core configuration. 
     It will therefore be apparent that the alignment between the first and second plurality of openings in the pre-die plate and the die plate can be critical because if the first openings are slightly misaligned with respect to the second openings, the core component will not be centered with respect to the second component, and the resulting fiber may have the aforesaid disadvantages. 
     When it is recognized that both the pre-die plate and the die plate are formed with an inordinately large number of openings extending therethrough, all of which are very small, it will be quickly apparent that the tolerances involved are quite close. Therefore a slight misalignment between these small openings is always possible. 
     Moreover, this problem is greatly exacerbated by the fact that the fiber components must be maintained in their molten state during their flow through the two plates, which therefore may reach also very high temperatures (up to 350° C.), still considering the different melting grades of the two components. 
     Since the plates are formed of steel, these elevated temperatures (and their inherent variations), cause the dimensions of the plates to change, either through expansion or contraction, and these changes can move one set of openings in one of the plates relative to the openings in the other plate, which can create a very undesirable misalignment of the two sets of openings. 
     Accordingly, there is a need in the art to provide a simple and reliable method and apparatus which will compensate for any misalignment between the openings in the two plates, and will insure that the core component will be centered with respect to the sheath component. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an apparatus is provided for making fibers or continuous filaments consisting of first and second components, such apparatus including a first plate having an inlet for receiving the first fiber component, and having a first plurality of openings through which the said first fiber component flows to an outlet end of the openings. A second plate is juxtaposed with said first plate and has a second plurality of openings therein which are generally axially aligned with the said first plurality of openings in said first plate, and the said second plate having a flow channel that permits the said second fiber component to flow to the second. openings and out through an outlet end of the said second openings. 
     A plurality of flexible hollow tube members are mounted to extend axially into the second plurality of openings with one end of each of the flexible tube members being located adjacent the outlet end of one of the first openings and with the other end of each of the flexible tube member being located adjacent the outlet end of the said second openings. The flexible tube members present a cross-sectional area less than the cross sectional area of the second openings, and they are sufficiently flexible to accommodate any misalignment between the said first and second openings without adversely affecting the flow of the first and second components. 
     In the preferred embodiment of the apparatus of the present invention, each of the flexible tube members has centering vanes located at the aforesaid other end thereof which extend outwardly and into engagement with the walls of the second openings, and these vanes are dimensioned to center such other end of the flexible tube member in the second opening, and to maintain such other end of each flexible tube member axially aligned with the second openings even if such one end of the flexible tube member is not axially aligned with the second opening. 
     Preferably, the flexible tube members are mounted in the first openings of the first plate at the outlet end thereof. 
     Also, in the preferred embodiment of the present invention, the second plate includes die openings adjacent the outlet end of the second openings and communicating therewith so that the second component flows from the second openings into the die opening, and the other end of each flexible tube member has a discharge opening directing the flow of the first fiber component into the die opening within the flow of the second fiber component to thereby form a sheath-core fiber or continuous filament. 
     The present invention also includes a method forming a fiber or a continuous filament from two fiber components comprising the steps of positioning a first upper plate having a plurality of first openings therein immediately adjacent a second lower plate having a plurality of second openings therein and a plurality of die openings in the bottom face thereof, with said first and second opening being generally axially aligned. The method includes the step of positioning a plurality of flexible hollow tube members so that one end of each flexible tube member is in communication with each of the first openings, and so that the flexible tube members extend into the second openings generally in axial alignment therewith, with each flexible tube member having a cross-sectional area less than the cross-sectional area of said second openings to form a flow channel therebetween. The same method includes the step of causing the flexible tube members to flex adjacent the upper ends thereof to accommodate any axial misalignment between said first and second openings. 
     The method also includes the steps of creating a first flow path for the first fiber component that extends through the first openings and through the interior of said flexible hollow tube members to be discharged from the flexible hollow tube members and through the die openings; and creating a second flow path for the second fiber component that extends through the second openings and around the exterior of the flexible tube members to be discharged from said second openings and through the die openings in a manner that surrounds the flow of the first fiber component through the die openings, to thereby form a sheath-core fiber or continuous filament. 
     In the preferred embodiment of the present invention, this method also includes the steps of disposing the lower ends of the flexible tube members at the bottom end of the second openings, and mechanically maintaining such lower end of the flexible tube members centered with respect to the second openings particularly maintaining the lower end of each said flexible tube members axially aligned with the second openings and the corresponding die openings, even if the upper end of the flexible tube members is not axially aligned with the second openings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical section view taken through an apparatus for forming two component fibers or continuous filaments that embodies the present invention; 
     FIG. 2 is a detail view taken along section line  2 — 2  in FIG. 1; 
     FIG. 4 is a detail cross-sectional view a sheath-core fiber formed with the core component offset from the center of the sheath component and from the center of the fiber; and 
     FIG. 3 is detail cross-sectional view similar to FIG. 4 but with core component centered. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Looking now in greater detail at the accompanying drawings, FIG. 1 is a diagramatic view taking along a vertical section through a preferred embodiment of the apparatus for making fibers or continuous filaments in accordance with the present invention. 
     The apparatus of the present mention includes a die plate  10  juxtaposed and beneath a pre-die plate  12 . A distribution system  14  is provided for distributing the molten polymers to such pre-die plate  12 . 
     In the preferred embodiment of the present invention, a complete die may be made up of two rectangular die plates positioned in side-by-side relation, with each rectangular component having a length of one to six meters, or more, and a width of approximately three hundred millimeters in the bottom surface of the die plate  10 , a plurality of die openings  16  are formed with one die opening  16  being positioned at the center of each five millimeter-by-five millimeter surface area on the bottom of the die plate  10 . However, it is to be expressly understood that the foregoing dimensions are merely representative of one typical embodiment of the present invention. Other dimensions can be used, depending on the application of the present invention. 
     The distribution system  14 , which is schematically illustrated in FIG. 1, includes distribution channels  18  through which a first molten polymer component A flows into a plenum  20 , and then through a first plurality of openings  22  to a second plenum  24 . Component A then flows vertically downwardly from the second plenum  24  through a plurality of vertically extending openings  26  which have an outlet end  28  on the bottom face of the pre-die plate  12 . The distribution system  14  also includes a second set of conduits  30  through which a second molten polymer component B flows to vertical openings  32  formed in the pre-die plate  12 . 
     The die plate  10  is formed with a relatively large open plenum  34  at its upper face, and this plenum  34  receives component B from the openings  32  in the pre-die plate  12 . The bottom portion of the die-plate  10  is formed with a plurality of vertically extending openings  36 , each of which is in open communication with the plenum  34 , and the bottom end of each opening  36  is in communication with one of the aforesaid die openings  16 . 
     When the die plate  10  and the pre-die plate  12  are juxtaposed as illustrated in FIG. 1, the vertical openings  26  in the pre-die plate  12  are generally axially aligned with the vertical openings  36  in the die plate  10 . 
     In accordance with the present invention, a flexible hollow tube member  38  is mounted in the bottom end of each of the first openings  26  in the pre-die plate  12 . The lower end of each flexible tube member  38  extends vertically into the second openings  36  in the die plate  10 , in axial alignment therewith. 
     The flexible tube members  38  are preferably formed of a thin stainless steel that provides the flexibility required of these tube members  38  as will be then explained in greater detail. It is to be understood that the hollow tube members  38  could be formed of any other suitable material. 
     The lower ends of the flexible tube members  38  have a cross-sectional area that is less than the cross-sectional area of the openings  36 . So, a flow channel  40  is provided between the exterior surface of the hollow tube members  38  and the interior surfaces of the vertical openings  36 . 
     Additionally, the bottom ends of the flexible tube members  38  are provided with a plurality of centering vanes  42  that extend outwardly and into an engagement with the walls of the openings  36 . 
     These vanes  42  are dimensioned in order to center the lower end of the flexible tube member  38  in the lower end of the corresponding vertical openings  36  and to maintain the lower end of the flexible tube member  38  axially aligned with the openings  36  even if the upper end of the flexible tube member  38  is not axially aligned with the openings  36 , as will also be explained in greater detail presently. 
     Centering vanes  42  may have a different shape in respect with the illustration shown in FIG. 1, for example they could have polygonal section, or others, with ends in engagement with the walls of the openings  36 . 
     Each of the flexible tube members  38  is provided with a discharge opening  44  located just beneath the centering vanes  42 , and the discharge openings  44  are located so to direct the flow of molten polymer therefrom into the center of an adjacent die opening  16 . 
     In operation, the first molten polymer component A, which is indicated in the drawings by the arrows shown in full lines, flows into the pre-die plate  12  from the distribution conduits  18 , at which point conventional filters (not shown) may be positioned to filter the molten component A. Component A then flows vertically through the openings  22 , then through the second plenum  24  and into the upper end of the openings  26  and downwardly through the interior of the hollow flexible tube members  38  until it is discharged from the discharge opening  44  into the die-opening  16  through which it exits the die plate  10 . 
     At the same time, a second molten component B, which is indicated in the drawings by the arrows shown in dotted lines, flows through the distribution conduits  30  to the vertical openings  32  and the pre-die plate  12 . Component B so reaches the open plenum  34  at the upper end of the die plate  10  then flows downwardly through the flow channels  40  between the hollow flexible tube members  38  and the openings  36 . 
     Component B collects at the lower end of the vertical openings  36 , and is discharged through the die openings  16  in a manner that surrounds component A as it is being discharged from the discharge opening  44  of the tube members  38  and into the die openings  16 . 
     Thus, when the components A and B exit the die plate  10  through the die opening  16 , they will form a sheath-core fiber or continuous filament with component A forming the core and component B forming the sheath. 
     Looking at FIG. 1, it will be noted that the openings  26  in the pre-die plate  12  must be axially aligned with the openings  36  in the die plate  10  to form a sheath-core fiber in which the core is centered with respect to the sheath, and with respect to the axis of the same sheath-core fiber. However, as discussed above, these openings  26  and  36  are very small in diameter, and even the slightest misalignment of the openings  26  and  36  can result in the core component being offset from the center of the fiber, as illustrated in FIG. 4, with all of the adverse consequences discussed above. 
     It will also be appreciated that the continuous flow of the molten components A and B through the die plate  10  and the pre-die plate  12  results in the temperature of both plates being at a high temperature level which can, and usually does, cause some distortion of the dimensions of the die plate  10  and the pre-die plate  12 , and in view of the close tolerances required for the alignment of the small openings  26  with the small openings  36 , any such temperature induced distortion can result in the aforesaid undesirable misalignment of the same openings  26  and  36 . 
     By virtue of the unique features of the present invention, the misalignment of the openings  26  and  36  can be accommodated without adversely effecting the centering of core component A with sheath component B. Most specifically, since the upper ends of the hollow flexible tube members  38  are disposed within the open plenum  34  they are free to move within the plenum  34  if, for whatever reason, the outlet ends  28  of the openings  26  become misaligned with the openings  36  in the die plate  10 . Moreover, the presence of the centering vanes  42  will assure that the lower end of the flexible tube members  38  will also be maintained centered with respect to the openings  36 , and the lower end will also be maintained in axial alignment with the die opening  16  even if the upper end of the flexible tube members are flexed as a result of some misalignment between the openings  26  and the openings  36 . 
     In this way the centering, or axial alignment, between openings  44  of flexible tube members  38  and openings  16  of the die plate  10 . Accordingly, the flexible tube members  38  will cause the two component fiber formed by the die plate  10  to always position the core component A at the center of the two component fiber as illustrated in FIG. 3 even if there is some misalignment between the small openings  26  and  36  that would otherwise form a two-component fiber as shown in FIG. 4 with the core component A offset from the center of the fiber. 
     The continuous filaments obtained through the method and apparatus of the present invention, are suitable in particular, to be used as staple fibers (cut fibers), spun bonding non-wovens, melt blown or other applications.