Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND MOLD FOR MAKING AN IMPROVED EGG CARTON
This invention relates to an improved egg carton, and to
methods o~ and molds for making it.
U.S. Patent 2,990,094 shows an egg carton with a latch of
the type in which a "button" on the latch flap extends through a
hole in the flat surface of the cover to latch the carton closed.
Problems were experienced with this type of egg carton because
persons picking the carton up by the cover inadvertently pushed the
protrusion out of engagement with the hole, thereby ùnlatching the
egg carton with disastrnus results.
Cartons o~ the type shown in U.S. Patent 37648,916 -
Commisso obviate this problem This latch flap has a locking recess
which includes a latch bar across the top thereof. The cover has
recesses which are complementary to the recess on the latch flap. A
hole is cut across the recess in the cover. This hole extends from
the flat surface of the front of the cover down into the recess,
across the recess, and back to the front surface of the cover. In
the closed position, the latching bar fits into this hole to hold
the cover in the closed position. This latching mechanism has the
advantage that it is recessed. Therefore, when the carton is
grasped by the cover, there is no possibility of inadvertently
unlatching the cover.
Egg cartons of this type are thermoformed from a sheet of
preheated polystyrene foam. In egg cartons of the type shown in the
Commisso patent, it is important that the hole in the cover extend
all the way from the front surface of the cover to the bottom of the
recess, and back to the front surface. Only when the hole is
completely extended in this manner, will the latching bar fit into
the hole to lock the carton. Because o~ this, cartons of the type
shown in the Commisso patent have heretofore been formed in two
steps. The first step is the thermoforming operation in which two
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mold members close to form the carton. The second step is a
punching operation which punches the hole in the cover. It is
desirable to eliminate the separate punching step so that the carton
is formed with a hole in the cover during the molding operation.
U.S. Patents 3,845,187 and 3,862,817 Dahlberg describe a
thermoforming method and molds for cutting a hole in the carton at
the same time that the carton is formed. An attempt is made to tear
the edges of the hole to form the portion of the hole between the
cover and the bottom of the recess so that the latching bar will
mate with the edge of the hole. Tearing plastic material is
unpredictable and results in many cartons with inoperable locks.
Furthermore, a torn edge on the hole is unsightly~
A more desirable hole is formed by the process and molds
shown in U.S. Patent 4,108,941 - Kermoian, 4,182,848 - Irwin and
4,143,111 - Irwin. As shown in these patents, dies in the male and
female mold members shear the plastic during the closing of the
molds to cut a hole in the cover.
It is an object of the present invencion to cut a hole in
the bottom of a recess in the cover of a carton during molding to
form a recessed latch which will not be inadvertently unlocked.
In accordance with the present invention, an egg carton has
a hole cut in an inwardly offset surface of a recess in the front
wall o~ a cover, which cut is in a plane transverse to the top of
the cover. A protrusion on the bottom surface of the recess in the
latch flap extends through a complementary hole in the inwardly
offset surface of the cover to latch the carton in the closed
position. The carton has the advantage of a recessed latch which is
not easily opened accidentally. It has the further advantage of
allowing the cutting of the hole in the cover during the molding of
the carton. This eliminates tearing of the cover or the requirement
of a separate step for punching out the portion of the cover between
the inwardly offset surface and the front surface of the cover.
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In accordance with another aspect of the invention, the
protrusion of the latch flap has a sloping surface angled at the
same angle as the beveled edge of the latch flap to aid in olosing.
The sloping surface of the protrusion terminates in a sharp undercut
which provides good closure strength, but the carton is easier to
open. The invention is carried out by closing a male mold member
and a female mold member on a preheated flat sheet of polystyrene
foam to produce a carton having a cover and a latch flap. A male
cutting key mounted on the male mold member has a cutting surFace
parallel to the closing motion between the male and female mold
members. A female cutting key is mounted in the female mold member
and has a flat cutting surface which is also parallel to the closing
motion between the male and female mold members. The cutting keys
in the male and female mold members are biased one against the other
during the closing motion o~ the mold members. The flat surface of
the cutting keys shear a hole in the cover transverse to the top o~
the cover during closing of the mold members. The mold has the
advantage of not requiring precise alignment of the male and female
mold members. Therefore, the cartons of the present invention can
be produced on existing molds, which frequently do not have close
fitting tolerances, by merely fitting the molds with the male and
female cutting keys of the present invention. Upon closure of the
mold members, the female cutting key engages a beveled edge on the
male cutting key. The engagement moves the male cutting key against
the bias in a motion transverse to the closing motion Therefore,
good registration between the flat cutting surfaces of the cutting
keys is obtained regardless of the closing tolerance between the
male and female mold members.
The foregoing and other objects, features and advantages of
the invention will be better understood from the following more
detailed description and appended claims.
In the Drawings:
Fig. 1 shows a portion of the latch flap and the cover
which has the latch of the present invention;
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Fig. 2 is a view of the carton in the closed position;
Figs. 3 and 4 are sectional views of the carton in the
closed and open position respectively;
Fig. 5A shows a carton of the type shown in the
aforementioned Commisso patent;
Fig. 5B iS a comparable view of the carton of the present
invention;
Fig. 6 is a partial cross-section through the male and
female mold members which are in the open position;
Fig. 7 is similar to Fig. 6 with the mold members closed;
Fig. 8 shows the male key and male key holder;
Fig. 9 shows the female key and female key holder;
Fig. 9A is a section on the lines A-A of Fig. 9;
Fig. 10 is a top view of the male mold member showing the
outline of the male key holder; and
Fig. 11 is a side view of the male mold member.
Referring to Figs. 1-4, the egg carton of the present
invention includes a bottom tray 11 formed to define a plurality of
cells for receiving eggs. A dished cover 12 is resiliently hinged
to the rear upper edge of the tray. It has a front wall 13, a top
14, a back wall and end walls fixed to the top. The front wall 13
slopes in a plane inwardly toward the top. A latching flap 15 is
resiliently hinged to the front upper edge of the tray 11 and with a
bias of the flap toward an outward position. Recesses 16 and 17 in
the front wall of the cover have a surface 18 which is inwardly
offset with respect to the front wall. A hole 19 in this surface is
cut in a plane which is transverse to the top 14 of the cover. A
recess 20 in the latch flap 15 complements the recess 16 in the
front wall of the cover. A protrusion 21 on the bottom surface of
the recess 20 extends through the complementary hole 19 in the
inwardly offset surface of the cover. This latches the carton when
it is in the closed position as shown in Fig. 3. The carton of the
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present invention has the advantage that when in the closed
position, the protrusion 21 is within the confines of the recess 16
so that it cannot be inadvertently unlatched by grasping the cover
of the carton.
The structure of the protrusion 21 is an improvement over
the button type latches shown in the aforementioned '094 patent.
The protrusion 21 has a sloping surface 21a which is angled at the
same angle as the beveled edge 15a on the latch flap 15. This
sloping surface terminates in a sharp undercut which forms the
latching surface.
The advantages of the present invention over the carton of
the Commisso patent are best demonstrated by comparing figs. 5A and
5B. In Fig. 5A a latch bar 22 at the top of the walled recess 23 in
the latch flap forms the male locking member. m e hole 24 in the
cover is cut from the ~ront surface of the cover to the back to the
inwardly offset surface 25, and then back to the front surface.
Only if the hole is cut completely to the front surface of the
cover, will the latch bar 22 fit through the hole to provide a
positive engagement. On the other hand, the hole 19 in the cover of
the carton of the present in~ention is flush with the inwardly
offset surface 18. This hole can be simply sheared during the
molding of the egg carton. Good latching is obtained with this type
of hole by reason of the protrusion 21 extending through the hole 19.
Referring to Figs. 6 12, the mold forming this egg carton
includes a male mold member Z7 and a female mold member 28. These
members are closed one with respect to the other on a preheated flat
sheet of polystyrene foam to form a carton cover, the outline of
which is shown in Fig. 7.
Q male cutting key 29 is mounted in a male key holder 30
which is in turn mounted in the male mold member 27. The male
cutting key 29 is biased toward the left by the spring 31. A cover
32 (Fig. 8) for the male cutting key 29 ensures that it moves only
; in a direction transverse to the closing motion of the mold members.
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A female key 33 is mounted in a female key holder 3~ which
is in turn mounted on the female mold member 28. The female cutting
key has a flat cutting surface 35 which is parallel to the closing
motion of the mold members. The male cutting key 29 has a mating
flat cutting surface 36 parallel to the closing motion of the mold
members. The male key has a beveled edge 37 along the surface which
first engages the female key during closing motion between the male
and female mold members. The engagement of the female key 33 with
the beveled edge 37 produces a motion of the male key toward the
~ight (Fig. 6) against the bias of the spring and transverse to the
closing motion between the male and female mold members. This
transverse motion is sufficient to ensure complete engagement
between the flat surfaces 35 and 36 of the male and female cutting
keys during further closing motion of the mold members. The bias
between these flat surfaces ensures a good shearing action in a
classic scissor-like motion in which the two cutting surfaces are
biased oblique to one another. The beveled edge and bias also
ensure that this action will be present regardless of the alignment
between the male and female mold members.
While a particular embodiment has been shown and described,
modifications are within the true spirit and scope of the
invention. The appended claims are, therefore, intended to cover
all such modifications.
