Patent Publication Number: US-2007119464-A1

Title: Enhanced earplug with bendable stiffener

Description:
CROSS-REFERENCE  
      This is a continuation-in-part of U.S. application Ser. No. 10/937,211 filed Sep. 09, 2004, which claimed priority from U.S. provisional patent application Ser. No. 60/502,789 filed Sep. 12, 2003. 
    
    
     BACKGROUND OF THE INVENTION  
      Earplugs are used to block environmental noise (but may pass other sound). Earplugs formed solely of soft resilient foam material are difficult to insert into the ear canal. When the front end of the earplug lies against the entrance to the ear canal and the rear end of the earplug is pushed, the foam earplug collapses. During such collapse, as shown at Z in  FIG. 15 , the front end of the earplug enlarges in diameter and does not move into the ear canal. It has been found that a core of stiffer material, as in the form of a rod, can be placed in a soft resilient foam body to help insert the foam body into the ear canal. U.S. Pat. No. 5,573,015 by Williams shows a foam body molded around a stiffer core by extrusion.  
      Although a rod-shaped elastomeric stiffener helps in earplug insertion, it makes the earplug stiffer against bending. Many people have ear canals that are curved, so an earplug inserted into one of the ears must bend to follow the curvature of the ear canal. The stiffener resists bending, causing forces on the sides of the person&#39;s ear canal and consequent possible discomfort to the person. An earplug with a stiffener to help insertion, wherein the stiffener was sufficiently stiff against column collapse but was easily bent by the walls of the ear canal to avoid discomfort, would be of value.  
     SUMMARY OF THE INVENTION  
      In accordance with one embodiment of the invention, applicant provides an earplug with a soft earplug body, a stiffener extending within much of the length of the body, and an earplug manufacturing method therefor, wherein the stiffener is axially stiff but allows the body to easily bend. A more bendable earplug is obtained by using a tapered stiffener, with its rear end wide and its front end narrow.  
      An earplug body can be molded in a cavity, with a mandrel extending along the axis to leave a stiffener inner cavity. When the mandrel is removed, an elastomeric stiffener material is poured into the inner cavity and allowed to solidify.  
      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 a rear and side isometric view of an earplug of one embodiment of the invention.  
       FIG. 2  is a partially sectional side view of the earplug of  FIG. 1 .  
       FIG. 3  is a sectional view of the earplug of  FIG. 2 , but with a modified stiffener.  
       FIG. 4  is a sectional view of a mold in which the earplug of  FIG. 3  is being molded.  
       FIG. 5  is a sectional view of another mold in which an earplug of the type illustrated in  FIG. 6  is being molded.  
       FIG. 6  is a partially sectional view of a pair of earplugs, each of the type shown in  FIG. 5 , and with a cord with opposite ends anchored in the earplugs.  
       FIG. 7  is an isometric view of an earplug with another form of stiffener.  
       FIG. 8  is an isometric view of a stiffener of the earplug of  FIG. 7 , which has a rear portion of enlarged width.  
       FIG. 9  is a sectional view of a mold, in which an earplug with a stiffener of the type shown in  FIG. 8  is being molded.  
       FIG. 10  is a sectional view of an earplug in a mold, with a stiffener of another embodiment of the invention.  
       FIG. 11  is a side view of an earplug with a plurality of stiffeners or stiffener portions spaced about a circle.  
       FIG. 12  is a sectional view taken on line  12 - 12  of  FIG. 11 .  
       FIG. 13  is a sectional view of an earplug similar to that of  FIG. 11 , but with stiffeners or stiffener portions of a different construction.  
       FIG. 14  is a sectional view of an earplug similar to that of  FIG. 11 , but with stiffeners or stiffener portions of a different construction.  
       FIG. 15  is a sectional view of an earplug fully inserted into an ear canal that is curved, and also showing how a purely foam earplug would collapse.  
       FIG. 16  is a sectional view of an earplug mounted at an end of a head band.  
       FIG. 17  is a sectional view of an earplug with a stiffener that has flanges.  
       FIG. 17A  is an isometric view of just the stiffener of the earplug of  FIG. 17 .  
       FIG. 18  is a sectional view of an earplug with a stiffener that has parts of different stiffness. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIGS. 1 and 2  illustrate an earplug  10  which has a body  12  of soft resilient foam and a stiffener  14  that is of stiffer material than that of the body and that extends part of the distance along the earplug axis  16 . The stiffener is constructed of elastomeric material, which is resilient material having a Young&#39;s modulus of elasticity of no more than 50,000 psi. It is possible to construct the body of a slow recovery foam which is resilient but with the recovery after rolling to a small diameter being delayed. The stiffener is useful during earplug insertion into a person&#39;s ear canal, by the person pushing against the rear end  20  of the earplug to force the front end portion  22  of the earplug, which seals the ear canal, to enter the ear canal. The earplug is elongated in front F and rear R directions, also indicated by arrows L. The stiffener prevents the body front end portion  22  from collapsing during insertion and thereby increasing in diameter. The stiffener  14  shown in  FIG. 2  is in the form of a rod with an elongated narrow hole  24  in its rear end. The body has a narrow hole  26  extending to the body rear end  20 . Except for the narrow body hole  26 , there is no indication that there is a stiffener in the earplug. The hole  26  is long and narrow enough, with a length in direction L more than the width in directions W and more than the breadth in directions B (both perpendicular to the length L) so the stiffener cannot be easily seen.  
       FIG. 3  illustrates an earplug  30  with a stiffener  32  that is elongated along the earplug axis and is therefore post-like. The stiffener has a wider rear end  34  than its front end  36  or middle  40 . The stiffener extreme front end  37  lies closer to the earplug front end  38  than to the earplug rear end  42 , and usually closer to the body front end than to the body middle. The wider rear end assures that the stiffener will receive the forward pushing force that a person applies to the rear end  42  of the body  44  during insertion into the ear canal, even if the person is careless about applying the force along the middle of the earplug rear end. The front end and middle are more likely to have to bend to follow a curved ear canal and their smaller diameters facilitate such bending. The wider, or larger diameter rear end should have a diameter H that is at least 50% greater than the front end (at a location before the curvature at the front end), with H actually being more than twice G and preferably two to four times G. G is taken rearward of a rounded end. When pushing the earplug rear end during insertion, it is desirable to turn the earplug about a quarter-turn to help insert the earplug. Such quarter turn is achieved by turning the finger that is pressing on the earplug rear end by a quarter turn. The larger diameter rear end of the stiffener makes it easier to twist the earplug. The stiffener is preferably gradually tapered in diameter, that is, the diameter gradually increases rather than increasing in steps, along a majority of the stiffener length. The stiffener outside surface preferably is angled by less than 10° to the axis  16  along most of the stiffener length. The stiffener is preferably of circular cross-section, but can have other cross sections such as a square or hexagonal cross section.  
       FIG. 4  shows a method by which the earplug of  FIG. 3  is formed. The body  44  of the earplug is molded in a mold cavity  50  formed between front or lower, and rear or upper mold parts  52 ,  54 . The stiffener  32  has been previously manufactured with a small diameter (or small width if the hole is of noncircular cross-section) hole  56  in its rear end. The top mold part has a downwardly-projecting pin  60  that has a lower part  62  that lies in the stiffener hole  56 . The pin has an upper part  64  that extends between the top of the stiffener and a bottom surface  66  of the upper mold part that molds the rear end of the earplug body. The stiffener is installed on the upper mold part as shown in  FIG. 4 , prior to the body molding process. To mold the body around the stiffener, foamable material is placed in the cavity  50  in the lower mold part (or foamable material is injected into a closed mold. Then the mold is closed, while the foamable material expands and fills the mold. A vent (not shown) allows air to escape. After the foam sets, the mold is opened and the pin  60  is pulled out of the stiffener, leaving the narrow elongated hole in the earplug. It is possible to fill the hole  26  ( FIG. 3 ) with material, but applicant prefers to not do that.  
      In one example, the earplug front portion has a diameter D of 0.50 inch (12.5 mm), the pin  60  has a diameter of 0.5 mm to 4 mm, such as 1.5 mm, and the hole part  64  between the rear end of the stiffener and the rear end of the body is longer than the pin diameter, such as 6 mm long. The pin extends more than its diameter into the stiffener hole  56  to closely control the orientation of the stiffener in the mold. The pin front end that lies in the stiffener during molding can have a few ribs to more easily provide a press fit that prevents the stiffener from falling in the mold cavity and that allows easy pin withdrawal. The soft elastic foam body has a durometer of 1 to 10, shore A, while the stiffener is preferably of the soft rubber type with a durometer of at least  30  shore A.  
       FIG. 5  illustrates an earplug  70  that is somewhat similar to that of  FIG. 4 , except that the stiffener  72  is formed by a tube (with or without a slot in one side) whose passage  74  extends most or all of the way though the length of the stiffener (and possibly to the body front end). A pin  76  with a front end  78  extends through a long length of the stiffener. The earplug is formed in a mold  80  in a way similar to the earplug of  FIG. 4 . However, the stiffener passage is long and the rear end  90  of the stiffener is flush with the rear end  92  of the body (or may be recessed, or may even extend slightly rearward of the body).  FIG. 6  shows that the earplug is intended to receive an end  94  of a cord  96 . The cord extends between two earplugs  100 ,  102 , with the ends  94  of the cord inserted into the tubular stiffeners in the earplugs and held therein as with adhesive, or with barbs on a stiffened cord end, or other cord attachment means such as ultrasonic welding, heat staking, etc. Such corded earplugs are used to minimize the possibility that a single earplug will fall into a vat of material being processed.  
       FIGS. 8 and 9  illustrate a stiffener  110  with a tapered post part  111  and with a radial (with respect to the earplug axis  112 ) projection  114  at its rear end. The projection  114  has recesses that form wings  115 . The wings form radially outermost locations  121 - 124  and gussets  126 . The locations  121 - 124  are clamped between upper and lower parts  130 ,  132  of the mold  134 . When foamable material is placed in the mold cavity  140 , the foam material which will form the earplug body, surrounds the stiffener, except at the four location  121 - 124 .  FIG. 7  shows the final earplug, which has four small stiffener locations such as  122 ,  123  that can be seen.  
       FIG. 10  illustrates an earplug  142  similar to that of  FIG. 4  but with a stiffener  143  having a wider rear end. The amount of stiffener material is minimized by forming the stiffer rear end with gussets  145  that support a wide circular rear end  146  on a post-like part  147 .  
       FIGS. 11 and 12  illustrate an earplug  150  with a stiffener  152  formed by a plurality of rods  161 - 164  of material that is stiffer than the material of the soft foam body  170 . Each of the rods is thin and therefore easily bent to avoid discomfort when the earplug is inserted into a curved ear canal, such as shown at  172  in  FIG. 15 . The four rods of  FIG. 12  lie on a circle  174  centered on the earplug axis  176  and there are spaces  178  between them. The rods are each partially supported by the foam body, to resist body collapse during insertion into the ear canal.  FIG. 13  shows a variation, wherein the stiffener includes two tube halves  180 , 182  of a tube centered on the earplug axis  184 . In both  FIGS. 12 and 13  the stiffeners each include a plurality of stiffeners, or stiffener portions, spaced apart along a circle that is centered on the earplug axis, with a plurality of spaces  178  or  190  between them.  
       FIG. 14  illustrates an earplug  200  with a stiffener  202  having a plurality of stiffener portions  211 - 214  that are spaced apart along a circle  216  that is centered on the earplug axis  220 . The particular stiffener  202  has a center portion  222  lying at the axis and four arms  224  that connect the center portion to the stiffener portions  211 - 214  that lie on the circle  216 . An advantage of the stiffener  202  is that the stiffener portions  211 - 214  and thin center portion  222  are easily bent when inserted into a curved ear canal. However, the stiffener portions  211 - 214  resist column collapse of the earplug body  224 . The stiffeners of  FIGS. 12-14  may be of constant cross-section along their entire lengths.  
       FIG. 16  illustrates an earplug  230  which is attached to an end of a head band  231 , such as the type shown in U.S. Pat. No. 6,138,790. The earplug has a body  232 , and has a stiffener  234  with a hole or passage  236 . A barbed post  240  has been forced into the stiffener passage. A rear end  242  of the post is anchored in the head band. An identical earplug and post lie at the opposite end of the band.  
       FIG. 17  shows an earplug  250  with stiffener  251  having a post  257  that is tapered, and with flanges  252 ,  254 ,  256  projecting radially outwardly (with respect to axis  260 ) and rearward R from the post. The stiffener is encased in a soft resilient foam body  262  by being molded in the body. The flanges, which are in the shape of truncated cones that extend 360° about the axis  260 , increase the blockage of noise. The stiffener is of material that is stiffer and more dense than the material of the body, and is preferably at least twice as dense. When noise encounters an interface between materials of different densities, more of the noise is blocked. The fact that the flanges extend at a radially outward-rearward incline helps in deflecting the flanges inwardly toward the axis as the earplug is installed in the ear canal. The flanges make the earplug overall more effective in blocking a range of sound frequencies. The flanges near the front end are of smaller diameters to minimize resistance to earplug compression during initial earplug insertion. The flanges add almost no resistance to bending of the earplug. In an earplug of 12.5 millimeter diameter, and therefore 6.25 mm radius (from axis  260 ), the flanges have a thickness of about 0.6 mm. At least one flange projects to a distance of at least 3 mm from the axis, and at least 2 mm beyond the stiffener portion that it projects from. The flanges preferably extend radially at least about half the radial distance between the outsides of the post and the outside of the body.  
       FIG. 18  shows an earplug  270  with a soft foam body  272  and with a stiffener  274 . The stiffener has two portions  280 - 282  of materials of different stiffness but with the materials of both portions being stiffer than the material of the body  272 . In one example the body is of foam having a stiffness of 2 shore A, the stiffener portion  280  has a stiffness of 10 shore A, and the stiffener portion  282  has a stiffness of 40 shore A. The stiffener is tapered in diameter, being widest at its rear end. The stiffest material such as material of stiffener portion  282  is tapered in thickness, being thickest at the rear end.  
      Thus the invention provides earplugs with soft resilient foam bodies (including slow recovery foam) and with elastomeric stiffeners bonded to the bodies by being molded one to the other. All of the illustrated earplugs are symmetric about their axis. An earplug with an axially aligned stiffener, is molded in a mold cavity, with the stiffener held by at least one pin that is preferably a centering pin, that extends into a hole at the rear end of the stiffener. The stiffener may or may not be concealed, especially where the stiffener is a tube that will receive an end of a cord that holds a pair of earplugs together. The stiffener may have a wide rear end, and narrow front end. A wide rear end may have locations that are clamped by parts of a mold to hold the stiffener in place. The stiffener may have a plurality of stiffener portions spaced along a circle that is concentric with the earplug axis. The stiffener may have flanges that help block noise. The stiffener may have radially inner and outer parts of different stiffness.  
      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.