Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND MOLD FOR MAKING AN IMPROVED EGG CARTON
This invention relates to an improved egg carton, and tomethods of 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 unlatching the
egg carton with disastrous results.
Cartons of the type shown in U.S. Patent 3,648,916 -
Commisso ob~iate 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 of 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 ~ttempt 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 ln 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 43108,941 - 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 bnttom of a recess in the cover of a carton during molding to
form a recessed latch whieh will not be inadvertently unlocked.
In accordance with one embcdiment of the present invention,
an egg carton has a hole cut in an inwardly offset surface of a recess
in the front wall of 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 sover 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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F-1021 ~3~
In accordance with another e~x~iment 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 ~lap to aid in closing.
The sloping surface of the protrusion terminates in a sharp undercut
which provides good elosure strength, but the carton is easier to
open. The invention is carried out by closing a male mold memoer
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 ~emale mold member
and has a flat cutting surface which is also parallel to the closing
motion between the male and ~male mold members. The cutting keys
in the male and female mold members are biased nne against the other
during the closing motion of the mold members. The flat surface of
the cutting keys shear a hole in the cover transverse to the top of
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 pre~ent 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. There~ore,
good registration between the flat cutting surfaces of the cutting
keys is obtained regardless of the closing tolerance bet~een the
male and ~emale mold members~
The invention, in one aspect, then, resides in a
carton adapted for the packaging of eggs and the like comprising~
(a) a bottom tray formed to define a plurality of cells
for reception of packaged articles and of a depth such that the
articles are enclosed thereby for a portion less than their
vertical dimension as packaged;
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-3a-
(b) a dished cover resiliently hinged to the rear
upper edge of the tray and having a front wall, a back wall,
and end walls fixed to each other and to a top for the co~er,
all of such dimensions situated so that the packaged articles
are substantially enclosed within the edges of the tray, the
front wall lying primarily in a plane sloping inwardly toward
the top;
(c) a latching flap hinged to the front upper edge of
the tray by resilient means biasing the flap toward an outward
position;
(d) a plurality of recesses in said fron wall of said
cover each having a surface which is inwardly offset with
respect to said front wall and lying in a plane sloping
upwardly towards said top, each recess having a hole in said
surface cut in a plane that extends perpendicular to the plane
of the top of the cover, and said hole being substantially
confined within said surface;
(e) a plurality of recesses in sai.d latching flap
engageable with respective recesses in said front wall of said
cover; and
(f) a plurality of protrusions at the free edge of said
latching flap opposite said flap hinge, each protrusion
extending through a respective one of the holes in the inwardly
offset surface of said cover to latch said carton in the
closed position.
The invention, in another aspect, resides in a
process for producing the previously defined carton, which
process comprises the following steps:
providing a relatively flat oriented sheet of
polystyrene foam;
preheating the sheet to at least its forming
temperature;
thermoforming the preheated sheet by bridging
together a male mold member and a female mold member to form
regions (a) and (c) to (f) of the carton and form the dished
cover (b) apart from the holes therein;
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shearing a hole in the surface of the co~er which
is inwardly offset with respect to the front wall of the
cover during thermoforming by relative movement between a
flat cutting surface of a male key mounted in said mold
member and a flat cutting surface of a female key mounted
in said female mold member, said movement being parallel
to the closing motion between said male and female members;
biasing said flat cutting surface of said male
key against said flat cutting surface of said female key
to produce shearing of said sheet between said key;- and
engaging an edge of said female cutting key with
a beveled edge of said male cutting key to move said male
key perpendicular to the closing motion between said male
and female mold members whereby engagement between the
flat surfaces of said male and female keys is obtained
regardless of the alignment between said male and female
mold members.
These aspects of the invention are disclosed, and
are also claimed, in Canadian Patent Application No.
409,094 - Daines - of which the present application is a
divisional.
The present invention, in a further aspect,
resides in a mold for producing the above-defined carton,
which mold comprises:
(A) a male mold member;
(s) a female mold member;
(C) means for closing the male and female mold
members on a preheated flat sheet of polystyrene foam to
form regions (a) and (c) to (f) of the carton and to form
the dished cover (b) apa.rt from the holes therein;
(D) a male cutting key mounted in said male mold
member and having a flat cutting surface parallel to the
closing motion between said male and female mold members,
(E) a female key mounted in said female mold
member and having a flat cutting surface parailel to the
closing motion between said male and female mold members;
-3c-
(F) said male cutting key ha~ing a be~eled edge
along the surface which first engages said female key
during closing motion between said male and female mold
members; and
(G) means for biasing the flat surfaces of said
male and female keys one against the other, the engagement
of said female key with said beveled edge producing a
motion of said male key perpendicular to the closing
motion between male and female mold members whereby
engagement between the flat surfaces of said male and
female keys is obtained regardless of the alignment
between said male and female mold members during the
closing motion of said mold members so that said
engagement cuts a hole in said cover perpendicular to the
top of said cover.
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 presend 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. ~A shows a carton of the type shown in the
a~orementioned Commisso patent;
Fig. 5B is a comparable view of the carton of
one aspect 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 one aspect of the present
invention i~cludes a bottom tray 11 formed to dcfine 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
1~ 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 ~lap toward an outward position. Recesses 16 and 17 in
the front wall of the cover have a surface 18 which is inward~y
offset with respect to the front wall. A hole lg 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 ~he bottom surface of
the recess ~0 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 ~hown in Fig. 3. The carton of one aspect of the
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present invention has the advantage that when in the closedposition, the protrusion 21 is within the confines of the recess 16
so that it cannot be inadvertently unlatched by grasping thP cover
of the carton.
The structure of the protrusion 21 is an impro~ement 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. The hole 24 in the
cover is cut from the ~ront surface of the cover to the back to the
inwardly of~set 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 invention 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 27 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.
A 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 34 whichis 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 3~ parallel to the closing motion of the mold
members. The male key has a beveled edge ~7 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
right (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 su~ficient to ensure com,olete engagement
between the flat surfaces ~5 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 w~ll be present regardless of the alignment
between the male and female mold members.
While particular embcdiments have been shown and described,
modifications are within the true spirit and scope of the
invention. The appended claim is, therefore, intended to cover all
such modifications.
