Abstract:
An earplug of the type that includes a soft foam body ( 14 ) and a more rigid core ( 16 ) that stiffens the body during its insertion into the ear canal, is mass produced so the front end ( 30 ) of the stiff core cannot rub along the surface of the ear canal during insertion. The core is elongated and bonded to the body, and the core has a front end ( 30 ) that is recessed from the front end ( 36 ) of the body, so the soft foam material of the body prevents the front end of the core from contacting the ear canal. The earplug can be mass produced by extruding the soft foam through an extrusion head ( 42 ), around the cores, with a long core device having been cut into the cores and with the extrusion ( 52 ) cut at locations to leave foam material forward of each core front end.

Description:
This application claims benefit of 60/497,377 Aug. 21, 2003. 

   BACKGROUND OF THE INVENTION 
   One type of earplug that is used to block intense noise from entering workers&#39; ear canals, includes a body of soft resilient foam material that is of greater diameter than the ear canal and that is inserted into the ear canal. Such insertion can be attempted by the worker placing the front end of the soft foam earplug body against the entrance to his/her ear canal, and then pressing forwardly against the rear end of the foam body. In practice, it is found to be almost impossible to insert the earplug by pressing against its rear end. Since the body front portion has a greater diameter than the ear canal, the earplug meets resistance, and since the body is soft it tends to buckle. One solution is to form the body of slow recovery foam material that can be rolled in the fingers to a small diameter, inserted into the ear canal, and held there until it expands. However, the earplug tends to become dirty if the worker&#39;s fingers are dirty. 
   It is found that insertion of a very soft body such as one formed of soft foam, can be facilitated by the use of a core that is much stiffer than the body and that has a front end lying deep in the body. U.S. Pat. No. 4,434,794 shows a core or stiffener that can be slid into a shell-shaped body to help its insertion. U.S. Pat. Nos. 5,573,015 and 6,659,103 show a stiffener lying within and bonded to a foam body and manufactured by extrusion. One problem encountered in the use of a stiffener or core such as the type shown in U.S. Pat. No. 5,573,015, is that there is a possibility that the front end of the core will rub against the ear canal during earplug insertion, especially if the person&#39;s ear canal is highly curved. Even if such rubbing is unlikely, people who are required to wear the earplug may be concerned about the possibility of such rubbing, especially if they press a finger against the front end of the earplug and notice the stiff core at the front end. An earplug with a stiffener, that avoided the possibility of the stiffener front end scraping against the wearer&#39;s ear during insertion, and that could be mass produced at low cost, would be of value. 
   SUMMARY OF THE INVENTION 
   In accordance with one embodiment of the present invention, an earplug and production method are provided that result in an earplug with a body of soft elastomeric material such as a soft foam, that can be readily inserted into the ear canal without soiling the earplug, and without danger of harm to the ear canal. The earplug includes a stiffener, or core that is much stiffer than the foam earplug body, and which extends along the axis of the body and which is bonded to the body. The core is elongated, with front and rear ends lying close, respectively, to the front and rear ends of the soft foam body. However, the front end of the core lies rearward of the front end of the body. This results in the front of the soft foam body preventing the front end of the core from touching the ear canal of even a highly curved ear canal. 
   The earplug can be formed by extrusion of a foamable material rearwardly though an extrusion head, while a stiffener core is also moved rearwardly through the extrusion head. The cores can be precut from a long core device, and moved though the extrusion head with a gap between subsequent cores. The extrusion is cut at locations slightly forward of the front end of each core, so extruded foam material lies in front of the front end of each core. In another process, a long continuous core device is moved though the extrusion head, within the foam that is being extruded, and the extrusion is periodically cut immediately after emerging from the head and while the foamable material is still expanding. This results in the foam expanding forward of the rod which is not foaming or otherwise expanding. 
   The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of an earplug of one embodiment of the invention. 
       FIG. 2  is a sectional view of the earplug of  FIG. 1 . 
       FIG. 3  is a partial sectional view of extrusion apparatus that can be used to mass produce earplugs of the type shown in  FIG. 2 . 
       FIG. 4  is a sectional view of an earplug of another embodiment of the invention, shown prior to complete expansion of the earplug body. 
       FIG. 5  is a sectional view of the earplug of  FIG. 4 , shown after expansion of the body. 
       FIG. 6  is an isometric view of an earplug of another embodiment of the invention, wherein a front portion of the core has been removed after molding. 
       FIG. 7  is a sectional view of an earplug shown prior to its complete manufacture, which has been cut from a solidified extrusion. 
       FIG. 8  is an isometric view of the earplug of  FIG. 7  after is has been finished by at least one cut across its front end to remove a front portion of the core. 
       FIG. 9  is a sectional view of an earplug of another embodiment of the invention, wherein the front end of an extrusion has been cut at an angle to its axis. 
       FIG. 10  is a sectional view of a person&#39;s ear canal, and shows an earplug as it begins the insertion process. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  illustrate an earplug  12  of one embodiment of the invention, which includes an earplug body  14  of soft resilient foam, and a stiffener or core  16  that extends along the axis  20  of the body. The body  14  has a front portion  22  of a diameter such as 0.4 inch to enter a person&#39;s ear canal, which has a diameter such as 0.3 inch, and form a sound-tight seal against it. The body is formed of a soft elastomeric material, having a durometer of 1 to 10, shore A. An elastomeric material may be defined as one with a Young&#39;s modulus of elasticity of no more than 50,000 psi. As mentioned above, such a soft body alone will collapse when the body front portion is pushed against the entrance of an ear canal. The core  16  is of material much stiffer than that of the body, such as a soft rubber which has a durometer of at least 30 shore A. However, the core is soft enough so it will bend when the earplug enters a curved ear canal. 
   The core is preferably made of a nonfoam elastomer such as rubber, and may be a solid post or a rubber tube that is hollow and filled with foam. The stiffness of the core material is more than twice that of the body, and its stiffness (per unit cross-sectional area) against compression between its opposite ends  30 ,  32 , is more than twice the stiffness of the body when the body alone is compressed between its opposite ends  34 ,  36 . The core  16  is elongated in the longitudinal direction M, with a length L more than twice its diameter D. The core diameter is small to allow the soft foam material of the body to be easily compressed in diameter. The core lies on the axis  20  of the body, which also extends in the longitudinal direction. 
   The front end  30  of the core  16  lies a distance A rearward R of the front end  36  of the body 14 . In  FIG. 2 , the core front end is not exposed because a body front part  38  lies directly in front of the entire area of the core front end  30 . The core is bonded to the body, which can be done by foaming a foamable body material around the core during an extrusion or other molding process. The earplug  12  can be inserted into a person&#39;s ear by the person placing the front portion  22  of the body against the entrance to the ear canal C, as shown in  FIG. 10 . The person presses against the earplug rear end  38 . The pressing force is transmitted by the core  16  (which is bonded to the body) to the front portion  22  of the body to press it into the ear canal. Applicant prefers that the rear end  32  ( FIG. 2 ) of the core lie a distance B of more than a millimeter forward of the body rear end, so the entire earplug has a soft touch to minimize apprehension of the person who will wear it. The core front end  30  is recessed a distance A of a plurality of millimeters from the body front end. The earplug  12  can be inserted into a person&#39;s ear by the person placing the front portion  22  of the body against the entrance to the ear canal, as shown in  FIG. 10 . The person presses against the earplug rear end  38 . The pressing force is transmitted by the core  16  (which is bonded to the body) to the front portion  22  of the body to press it into the ear canal. Applicant prefers that the rear end  32  ( FIG. 2 ) of the core lie a distance B of more than a millimeter forward of the body rear end, so the entire earplug has a soft touch to minimize apprehension of the person who will wear it. The core front end  30  is recessed a distance A of a plurality of millimeters from the body front end. 
     FIG. 3  illustrates apparatus  40  for producing earplugs of the type illustrated at  12  in  FIGS. 1 and 2 . The apparatus includes an extrusion head  42  that extrudes largely liquid foamable material  44  though a die opening  46  to form an extrusion  52 . At the same time, cores  16  are fed into the opening  46  to lie within the earplug bodies  14 A as they are extruded.  FIG. 3  shows blades  50  which are used to sever the extrusion  52 . The apparatus includes a feeder  60  that feeds cores that each have a length L of about two-thirds inch (17 millimeters), into the extrusion head opening  46  to lie in the earplug bodies  14 A as they are extruded. The blades  50  are operated to sever the extrusion  52  whenever a predetermined length of extrusion such as one inch, projects out of the extrusion head. 
   The feeder  60  feeds cores into the extrusion  52  at intervals synchronized with operation of the blades  50 . The synchronization assures that the opposite ends  30 , 32  of each core lies within the body  14 A, or at least that the core front end  30  lies recessed from the front end of the earplug body. In  FIG. 3 , applicant shows a tube  62  containing cores cut from a core device  16 B to the proper length and being pushed in the rearward extrusion direction R along the tube. Grippers  64  hold each core such as core  16 A for a short period of time and release it to lie in the proper position within the earplug body  14 A as the body is extruded.  FIG. 3  also shows a few fins  66  that help guide each core to position it at the axis or middle of the extrusion opening  46  while allowing the foamable material  44  to extrude easily into the opening. It is also possible to use a device that grips and pushes each core forwardly and releases it, or to use a continuous core device and to repeatedly cut it a short distance before the extrusion opening. The position of the leading end of each core can be detected within the soft foam extrusion, as by ultrasonic or x-rays, or by applying magnetic or metal material to an end of each core for detection. This facilitates cutting of the continuous extrusion to leave earplugs with core front ends consistently spaced from the body front ends by a distance of a few to several millimeters. 
     FIGS. 4 and 5  illustrate an earplug at different stages of its manufacture. At  80 A in  FIG. 4 , the earplug is shown when it is initially molded, as when it emerges from an extrusion head opening and is severed at the head. The earplug ends are slightly rounded as a result of the extruded foam material starting to expand.  FIG. 5  shows the earplug at  80  after its foam material has fully foamed and the earplug has cooled to room temperature. The core at  84 A in  FIG. 4  is shown as it lies within the body  86 A immediately after extrusion and cutting. The material of the body  86 A has not fully foamed. The body at  86  ( FIG. 5 ) in the finished earplug  80  has expanded to a larger length than the core, resulting in the ends of the core becoming recessed in the body. As mentioned above, this avoids the possibility that the core front end will rub against the ear of the wearer during earplug insertion. 
   The earplug illustrated in  FIG. 5  can be produced in the manner shown in U.S. Pat. Nos. 5,573,015 and 6,659,103 where a continuous core device is fed through an extrusion die opening around a foamable material, to form an extrusion from which earplugs are cut off, as by the blades  50  of  FIG. 3 . The extrusion is cut very close to the extrusion die whenever a given length (e.g. one inch) of extrusion lies forward of the extrusion head opening. In the present invention, the body expands in length (and usually also in diameter) after being cut to result in a core with a front end that is recessed from the front end  92  of the earplug body. In  FIG. 5 , the core front end  90  is exposed, because it lies at the end of a passage  94  in the body. 
     FIG. 6  illustrates an earplug  100  which is altered after being produced by one of the methods described in U.S. Pat. No. 5,573,015. The earplug is initially produced with a body of soft elastomeric material, preferably a foam, and with a core that is stiffer in compression along its front-to-rear length than the body. The core front end initially lies adjacent and almost flush with the front end of the body. The front end of the body is preferably rounded as in  FIG. 5 , although it can be flat as in  FIG. 7 . Applicant recesses the core front end by applying a tool to the core front end to remove some of the core initial front end. The core front end can be removed as by a rotary cutter that cuts away core material (and a little body material), or a hot poker that melts core material, to leave the core front end  108  recessed.  FIG. 6  shows substantially only the core front portion cut away, to leave a core front end that is recessed from the body front end.  FIG. 8  shows a pair of cross-cuts  130 , 132  formed across the front of an earplug  120  to leave a core front end that is recessed from the body front end. 
   Instead of forming each earplug by extrusion, it is possible to form each earplug by static molding wherein foamable material is injected or placed in a mold that contains a core with its front end recessed from the body that is to be molded around the core. 
   Applicant prefers that the rear end of each core lie about flush with or slightly recessed from the rear end of the body. If the core projects rearward of the body rear end, applicant prefers that the core not project more than about three millimeters rearward of the body rear end, so the projecting core does not interfere with pushing of the earplug into the ear canal. With the core rear end lying flush with or slightly recessed from the body rear end, a person can insert the earplug by pressing forwardly against the rear end of the earplug with the index finger or thumb, instead of requiring the person to grasp a rearwardly projecting core end and push it forward with possible flexing of such protruding core part.  FIG. 3  shows, in phantom lines, the core positioned so the rear end at  32 A lies about flush with the body rear end  38 . 
     FIG. 9  illustrates an earplug  140  with a front end cut at an angle X of at least 30° to a plane that is perpendicular to the earplug axis. This results in a flap  146  that can be bent over at  146 A to largely cover the front end  150  of the core  152 . 
   Thus, the invention provides a low cost earplug and production method, wherein a longitudinally elongated stiffener, or core lies in a soft elastomeric, preferably foam, body of the earplug, without danger that the front end of the stiff core will rub against the wearer&#39;s ear canal during initial insertion of the earplug into the ear canal. The core front end is recessed to lie rearward and preferably a plurality of millimeters rearward, but not more than about 1 centimeter, of the front end of the earplug body. In one earplug, the core front end is covered by body material, while in another earplug the core front end is exposed at the end of a passage. The earplugs with recessed core front ends can be manufactured at low cost by extrusion, by feeding precut cores into an extrusion head while foamable body material is extruded around the core. The core also can be recessed after an extrusion containing a continuous core device has been extruded and cut into lengths of about one inch each, by relying on an expanding body or by cutting away the front portion of the core. 
   Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.