This invention relates to an improved egg carton, and to methods of and molds for making it.
U.S. Pat. No. 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. Pat. No. 3,648,917--Commisso obviate this problem. The 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 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. Pat. Nos. 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. Pat. No. 4,108,941--Kermoian, U.S. Pat. No. 4,182,848--Irwin and U.S. Pat. No. 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 invention 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.