Molded foam earplug and method for making same

A bullet-shaped molded foam earplug is provided with a cavity extending from the flanged base axially into the earplug. The cavity provides the earplug a lower equilibrium pressure making the earplug more comfortable. The earplug is formed in a mold having a base containing a plurality of spaced apart cavities. A top plate having a plurality of pins is fitted onto the base such that the pins enter the mold and define the cavity of each earplug.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the field of earplugs and more 
particularly to the field of molded foam earplugs. 
2. Description of the Prior Art 
Foam earplugs have been developed which fit comfortably in the ear and 
provide desired sound attenuation. Examples of these earplugs are 
disclosed in U.S. Pat. No. 3,811,437 to Ross Gardner, Jr. which later 
reissued as U.S. Pat. No. Re. 29,487. Gardner teaches that a variety of 
resilient polymeric foams can be used. The foam has a sufficiently high 
concentration of organic plasticizer which permits the plug to be 
compressed and inserted into the ear canal. After insertion the plug 
recovers to exert an equilibrium pressure within the comfort range of the 
wearer. Louis Wood in his U.S. Pat. No. 4,158,087 discloses a 
polyurethane, latex foam which can be used for foam earplugs. Following 
the teaching of these patents, several companies have made and sold 
resilient foam earplugs. 
Resilient foam earplugs have been made in a variety of shapes. Cylindrical 
earplugs are commonly used as are generally conical, and bullet-shaped 
plugs. The bullet-shaped plugs are sometimes provided with a concave 
flanged base which does not go into the ear canal. The only constraint to 
the shape of the plug is that the plug must be able to be compressed to a 
size smaller than the ear canal so that the plug can be inserted into the 
ear canal, there expand to seal the ear canal and exert a comfortable, yet 
effective, pressure against the wall of the ear canal. 
Foam earplugs have been punched from sheets of foam and molded. In order to 
produce an earplug with a contoured shape, it is preferable that the plug 
be formed in a mold. Cantor in U.S. Pat. No. 2,441,866 discloses a bullet 
shaped rubber earplug having a hollow interior. The Cantor earplug cannot 
be radially compressed. If one exerts a radial force on the Cantor 
earplug, the wall of the earplug will bulge in a direction normal to the 
force or the wall will buckle. In either event, the circumference of the 
earplug will not change. A bulged Cantor earplug cannot be inserted into 
the ear canal unless it buckles. If a buckled Cantor earplug is inserted 
into the ear canal, the buckle will remain and the ear canal will not be 
completely sealed. Cabot Corporation has made and sold a foam earplug 
similar in shape to the Cantor rubber earplug. Like Cantor, this was a 
push-in type plug that could not be radially compressed for insertion into 
an ear canal. 
When a foam earplug is formed in a mold, there is a tendency for the foam 
to adhere to the mold surface and remain in the cavity of the mold. This 
tendency prevents easy removal of the molded foam from the mold cavity 
after formation. The use of pins which are suspended from a top plate and 
inserted into the cavity of the mold have been tried for some kinds of 
molded products. However, all too frequently, the pin will tear the molded 
product during removal from the mold. The art has not used pins in the 
molding of earplugs. Nor has the art recognized that pins of certain 
dimensions can be used to create a beneficial cavity in a molded slow 
recovery foam earplug. 
SUMMARY OF THE INVENTION 
I provide a molded foam earplug having a beneficial central cavity. The 
earplugs of the present invention are bullet-shaped. My earplug mold has a 
plurality of cavities into which pins suspended from a top plate of the 
mold are inserted. The pins can have a variety of shapes and extend from 
about 50% to 95% of depth of the mold cavity. Foam earplugs made from my 
mold will, therefore, have a substantial inner cavity. A foam earplug 
containing the cavity exerts less pressure on the ear canal than an 
earplug made of the same foam but having no cavity. Consequently, the 
cavity containing earplug is more comfortable. 
Other objects and advantages of my earplug and the mold for making same 
will become apparent from a description of certain present preferred 
embodiments therefore shown in the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIGS. 1 and 2, earplug 10 is generally bullet shaped having an 
end 12 adapted for insertion into the ear canal and a flanged base 14 
coextensive with the end 12 and adapted to provide means for removing the 
earplug 10 from the ear canal. Cavity 16 extends into earplug 10 from base 
14. In the embodiment of FIG. 2, cavity 16 is also bullet-shaped. 
Preferably, earplug 10 is produced by injecting the constituents of a 
resilient foam into a three piece mold 18. As shown in FIGS. 3 and 4, mold 
18 contains a plate 19, and center portion 20 and top 21 which together 
form a base. The center portion 20 has a plurality of cavities 22. 
Cavities 22 have the desired bullet-shape of earplug 10 and have a vent 
24. Top plate 21 fits onto center portion 20 to form a closed mold. 
A pin 30 is provided to extend from a top plate 21 and fit into each cavity 
22 of mold 20. Pin end 32 is sized and configured to correspond to the 
desired shape of cavity 16 of earplug 10. End 32 is both thinner and 
shorter than cavity 22. Flange 34 can be provided on pin 30 so that when 
the mold is opened the formed plug will remain on pin 30. Although the 
pins can be used to ensure ease of removal of the earplugs from the mold, 
it should be noted that the important function of the pins is to produce a 
cavity allowing for improved comfort of any foam earplug over that which 
it would have had being identical but without the cavity. 
After the foam ingredients have been provided in each cavity of mold 20, 
the top plate 21 is lowered and pins 30 are inserted into cavities 22. The 
ingredients react to form a foam. After the plugs 10 have been formed, the 
top plate 21 is lifted from the center portion 20 of the mold 18 which 
removes pins 30 from cavities 22. Because of the configuration of the end 
portion 32 and flange 34 of pin 30, plug 10 will remain attached to pin 30 
after the top half 21 and attached pins 30 have been removed from cavity 
22. Because foam plug 10 is deformable, the plug is easily removed from 
pin 30. This process is an improvement over the prior art wherein the plug 
10 remained in the cavity of the the mold, thereby making removal of the 
plug from the mold a time consuming process. 
As shown in FIGS. 5 thru 8, one can have a variety of cavity shapes and 
sizes each having associated advantages. The earplug 10 of FIG. 5 has a 
straight, shallow cavity 40. This cavity extends about 50% of the length 
of the earplug. The earplug of FIG. 5 can easily be stripped from the pin 
(not shown) used to form the cavity 40. Additionally, that pin will not 
interfere with foam formation during molding of the earplug. In the 
embodiment of FIG. 5 I also provide a concave base 42 on the earplug. 
The earplug 10 of FIG. 6 has a deep cavity 44 which extends about 95% of 
the length of the earplug. The wall 45 of cavity 44 is tapered so that the 
diameter of cavity 44 decreases as you move toward the tip or nose of the 
earplug. A flanged portion 46 is provided near the base of cavity 44 which 
then necks down to a cylindrical channel 48. That smaller channel 48 is 
less noticable than an opening which would have been made if sloped wall 
45 continued through the flanged base of the earplug. The pin used to make 
the cavity of the earplug of FIG. 6 would be identical to cavity 44, 
flanged portion 46 and channel 48. That pin has two important advantages. 
The sloped portion of the pin which defines wall 45 will aid polymer flow 
during foaming. The flanged portion will cause the earplug to adhere to 
the pin when the mold is opened. 
A frusto-conical cavity 50 with small channel 48 is provided in the earplug 
of FIG. 7. The pin used to form cavity 50 would have a sloped portion to 
define wall 51. That sloped portion would aid polymer flow during forming. 
The pin would also have a land to define wall 52. When the mold is opened 
the land would cause the plug to adhere to the pin. 
In the earplug of FIG. 8 a small channel 48 opens into a diamond shaped 
cavity 54. The pin used to form the diamond shaped cavity would have a 
first sloped portion to form wall 53 and a second sloped portion to define 
wall 55. During foaming the polymer should flow readily around these 
sloped portions. When the mold is opened the earplug of FIG. 8 should 
adhere to the pin that forms cavity 54. But, the sloped pin portions 
should permit easy removal of the plug from the pin. Indeed, removal from 
the pin should be easier than removal of the earplugs of FIGS. 6 and 7. 
The embodiments shown in the drawings illustrate that the pin can be made 
so as to either ensure that the plug mechanically adheres to the pin thus 
enhancing earplug removal from the mold or the pin can be made so as to 
release from the earplug with relative ease. This may be accomplished by 
making the pin tapered, of substances enhancing the release such as 
polypropylene, polyethylene, teflon and the like or alternatively by use 
of mold release agents such as waxes, silicones, fluoroplastics, metallic 
stearates, soaps, polyethylene, fine particles of talc and many 
proprietary blends of chemicals. 
Generally, the pin should be long enough so as to be at least 50% of the 
total length of the earplug, up to a length that terminates at or within 
the hemispherical like non-functioning tip of the bullet shaped structure 
without coming so close to the tip so as to allow decreased attenuation 
for any user. It is preferred to have the pin length between 60 to 90 
percent of the total plug length. The cavity should have a diameter of 
sufficient size so that the earplug does not bulge when radially rolled 
down between the thumb and forefinger of a user. By this is meant that the 
earplug can be radially rolled down without the cavity flattening to a 
closed position such that it causes the earplug to form a large wrinkle or 
fold. The absence of a wrinkle or fold is essential to ensure complete ear 
canal sealing, i.e. maximum sound attenuation, upon insertion of the 
earplug into a user's ear canal. In other words, to ensure maximum comfort 
without detracting from desired sound attentuation, the cavity diameter 
should be as large as possible without causing the earplug to lap or 
crease when being rolled down. Generally, I found that about 0.13 inch 
diameter is suitable. Depending upon the material and earplug construction 
a diameter of about 0.19 inches will also work. For an earplug of 0.46 
inches in diameter a cavity diameter from about 0.125 to 0.1875 (1/8 to 
3/16) inches is acceptable. 
The resulting molded earplug 10 possesses desired compressibility and 
recovery properties because of its unique structure. Because there is an 
absence of foam material in cavity 16, sidewalls 12a of earplug 10 can be 
readily compressed. When compressed, earplug 10 can be easily inserted 
into the ear canal and allowed to expand therein. Cavity 16 lowers the 
pressure exerted by sidewalls 18 against the ear canal making the earplug 
more comfortable. 
In order for the earplug 10 to function properly, it should have a diameter 
somewhat greater than that of the average adult human ear canal. For 
example, an average diameter between about 3/8 inch and about 3/4 inch is 
generally acceptable. Optimally, the average diameter of earplug 10 is 
between 7/16 inch and 9/16 inch. 
Foam earplugs with and without cavities were tested to determine the effect 
of the cavity upon equilibrium pressure exerted by the earplug on the ear 
canal. The tested foam earplugs had a length of about 0.9 inch, a flange 
diameter of about 0.7 inch, and an average diameter of the functional 
portion of about 0.46 inch. In order to aid collection of accurate data 
the flanges were cut off. 
The cut foam earplugs were stored overnight at 50% relative humidity and 
21.degree.-24.degree. C. After rolling the foam earplugs down by twirling 
between the thumb and forefinger for 20 seconds they were inserted between 
parallel plates spaced at a distance of 0.268 inch and the equilibrium 
force, in grams, was measured. Each earplug was measured four times, the 
results averaged and corrected for small weight differences encountered 
from cutting. 
Experimental results in Table I show foam earplugs with shallow 0.125 inch 
diameter cavities yield about 17% lower exerted force. Foam earplugs with 
the cavity extended 0.109 inch further reaching to about the point where 
the spherical earplug tip begins, shows about 30% lower exerted force. 
Earplugs exerting lower force will be more comfortable. 
I have found that the foams disclosed in Gardner Reissue Pat. No. 29,487 
and Wood U.S. Pat. No. 4,158,087 can be used to form a molded earplug in 
accordance with this invention. 
TABLE I 
__________________________________________________________________________ 
Equilibrium Force Measurements for Foam Earplugs 
With and Without Cavities 
Orig. Wt. (gms.) 
Wt. (gms.) 
Run (Equilibrium Force) 
Wt.* 
Wt. (gms.) 
50% RH 
Cut 1 2 3 4 Ave. 
Corr. 
SD 
__________________________________________________________________________ 
With 
Shallow 
Cavity 
Plug # 
1 0.4747 
0.4734 
0.2855 
78.32 
78.52 
76.10 
77.57 
77.63 
80.59 
2 0.4757 
0.4759 
0.3009 
78.66 
82.30 
80.65 
82.25 
80.97 
78.25 
3 0.4713 
0.4719 
0.2944 
77.60 
79.82 
76.83 
80.11 
78.59 
78.23 
4 0.4736 
0.4726 
0.2929 
79.99 
76.18 
77.81 
79.68 
78.42 
78.61 
0.98 
Ave. 0.2934 78.92 
Without 
Cavity 
Plug # 
1 0.4951 
0.4951 
0.3034 
100.56 
97.27 
101.77 
103.21 
100.70 
100.85 
2 0.4921 
0.4917 
0.2820 
78.88 
77.91 
79.45 
79.27 
78.88 
93.83 
3 0.4945 
0.4936 
0.2970 
85.86 
85.05 
86.60 
84.86 
85.59 
89.97 
4 0.4981 
0.4964 
0.3096 
94.64 
98.33 
97.47 
97.57 
97.00 
92.89 
5 0.4962 
0.4874 
0.3261 
100.35 
98.58 
98.55 
99.15 
99.16 
93.56 
6 0.4975 
0.4872 
0.3035 
107.46 
108.69 
109.43 
110.74 
109.08 
99.23 
Ave. 0.3036 95.06 
3.77 
With Cavity 
0.109" 
Deeper 
Plug # 
1 -- 0.4767 
0.2851 
69.21 
68.56 
69.39 
69.68 
69.20 
69.66 
2 -- 0.4752 
0.2888 
64.19 
64.31 
62.95 
64.43 
63.97 
63.57 
Ave. 0.2870 66.62 
3.05 
__________________________________________________________________________ 
For example, a polyvinyl foam was used to form earplug 10. The mold 20 was 
designed such that cavity 22 has a depth of 1.104 inches and an average 
diameter of 0.525 inches for the tapered cylinder section of the 
bullet-shaped portion 12. Upper base 14 has an average diameter of 0.774 
inches. In order to provide earplug 10 with the desired resilience 
characteristics, end 32 of pin 30 had a length of 0.1965 inches and an 
average diameter of 0.143 inches. Flange 34 had a diameter of 0.250 
inches. 
Use of the mold 18 described above produces an earplug 10 having a length 
of 0.894 inches and an average diameter of 0.454 inches. The diameter of 
flanged base 14 is 0.696 inches. Cavities of two depths were made. Both 
cavities had an average diameter of 0.130 inches. They had a depth of 
either 0.442 inches or 0.559 inches. These depths are about 50% and 63% of 
the plug length. Such an earplug 10 provides a comfortable fit within the 
ear canal of the wearer and was found to be highly effective in 
attenuating the transmission of 125-8000 Hertz. 
While I have described certain presently preferred embodiments of my 
invention, it is to be distinctly understood that the invention is not 
limited thereto and may be otherwise variously practiced within the scope 
of the following claims.