Containers are used for storing various types of volitile liquids, for example, chlorine. Packaging conditions, changes in ambient temperature, as well as other factors can cause the creation of gas fumes within the container and an increase of internal pressure. It is necessary to vent the container to avoid the explosion or implosion caused by the increased internal pressure or vacuum. At the same time, it is necessary to perfect sufficient sealing about the container opening to insure safety from undesirable leakage and spilling from the container.
Various can and container top venting caps have been derived. For example, the U.S. Pat. No. 30,585 to Paddock, patented Nov. 6, 1860, discloses a can including a lid having a valve guarded aperture communicating outwardly with an exhaust or vapor chamber which in turn communicates with a sealing cap. The U.S. Pat. No. 1,467,706 to Collins, issued Sept. 11, 1923, discloses a can top vent including a cap having a hole through its top wall located centrally thereof covered by a plate fixed to the outer surface of the top wall. The place has a convolute corrugation formed therein, the outer end of which terminates at the edge of the plate which is preferably a disk shape while the other end terminates substantially in the center of the plate. The corrugation produces a convolute air channel with an inlet at its outer end which communicates with the atmosphere while the inner end of the corrugation overlies the hole in the cap so that the inner terminus of the channel communicates with the hole to complete the communication between the interior of the container and the atmosphere.
The U.S. Pat. No. 4,545,498 to Schmid, issued Oct. 8, 1985, discloses a container with a lid for effervescent products. The lid has openings for the escape of gas. A layer, covering the opening is affixed to the surface of the lid. A passage leads to the exterior and is connected with the openings disposed between the layer and the lid.
A problem exists with direct openings between the interior of the container, through a lid and passageway, to an exhaust. Tilting or inadvertent shaking of the container can results in spilling of the contents through the opening and passageway. It has been found that hydrophobic membranes can be utilized which allow the passage of various gases for decreasing the interior pressure of the container while perfecting a seal for containing a liquid. For example, the U.S. Pat. No. 3,951,293 to Schulz, issued Apr. 20, 1976, discloses a gas permeable liquid closure for containers of liquids or solids which emit or absorb gas. The closure includes a film of unsintered tetrafluoroethylene. The film is supported across an opening of the container by a perforated cap or a perforated sealing diaphragm which is disposed on either one or both sides of the film. Problems have arisen with the use of hydrophobic membrane layers in sealing caps. The hydrophobic membranes are most often quite fragil and are unable to perfect a seal between a cap and the lip of an opening of a container. The membrane can be damaged during closure of the cap so as to not perfect a hermetic seal.
Additionally, most container caps are shipped in bulk packages. During shipping, the caps take a random position within a bulk package. Depending upon the ratio of the size of the skirt of the cap to the diameter of the base of the cap, there remains the possibility that a corner of one cap can enter the skirt of another cap so as to contact and damage the membrane.
The present invention provides a solution to the aforementioned problem by providing a protective filter cap which can effectively perfect a hermetic seal yet is able to vent internal pressures, and additionally avoids damage during shipping.