VENTING COVER AND CONTAINER WITH SUCH VENTING COVER

The present invention relates to a pressure release container with a spout opening, a neck along the periphery of the spout opening, and a venting cover comprising a body plate to cover the spout opening, the body plate having a vent opening and having arranged along its periphery a flange with an inner peripheral surface provided with fastening means to cooperate with corresponding fastening means on the outer face of the neck, wherein the vent opening is covered by a gas permeable filter.

Such containers can typically be used for compositions which are liable to exothermic decomposition. Owing to this slow decomposition with emanation of a gas capable of creating, over a period of time, a dangerous over-pressure in the container, such compositions cannot be held in hermetically closed containers. Among these materials are peroxide formulations, optionally dissolved in so-called phlegmatizers - typically hydrocarbon solvents - or in aqueous solutions, emulsions or suspensions. Typical examples of such peroxide materials are hydrogen peroxide or mineral peroxides such as the aqueous solutions of monoperoxysulphuric acid or liquid organic peroxides. All these peroxides permanently give off small quantities of gas such as oxygen, for instance. In order to avoid dangerous over-pressures in the enclosures of such products, these containers are provided with porous filters which are permeable to the gases and tight as concerns the liquids. Past the filter, the gases are discharged via one or more apertures in a closing cap.

US 4,853,013 discloses a vent cover with a filtering structure for a container that may hold dangerous materials such as liquid organic peroxides. It contains a cap and a filtering structure. In normal operation, gas driven off by the liquid in the container passes through the whole of the filtering structure and escapes through the vent means. The filtering structure contains two filters that are permeable to gas and impermeable to liquid. Such venting systems have a rather complicated structure and are therefore expensive to make.

AU 9 341 259 discloses a pressure vent for the storage and transport of, e.g., organic peroxides in the form of a cap with a small hole occluded by a membrane of porous PTFE in intimate contact with a layer of porous polyethylene foam.

PTFE filters in screw cap vent covers are disclosed in EP 0 759 401 A.

The object of the invention is to provide a venting system of a simplified construction, which is particularly suitable for storing peroxide formulations or other materials liable to exothermic decomposition.

The object of the invention is achieved by a container according to the opening paragraph, characterized in that the gas permeable filter is a sheet fixed between the fastening means of the neck and the flange. This way, a very effective low-cost venting construction is obtained which can be easily assembled.

The sheet can for example be a foil of a plastic material, such as low density or high density polyethylene (LDPE, HDPE), polyvinylchloride, polypropylene or the like. The thickness of the sheet can be for instance between about 5 micrometres and about 0.5 mm, e.g. between about 10 micrometres and about 0.1 mm.

To make the sheet permeable for gas, the sheet can for example be perforated. The pore diameter of the perforations can for instance be between about 10 micrometres and about 2 mm, e.g., between about 0.1 mm and about 1.5 mm.

To prevent spillage of the content, the permeable sheet can for example be built of two or more layers of perforated sheet. Preferably, these are installed in such a way that the perforations of one layer are not in line with the perforations in the other layer.

The venting cover can for example be a screw cap. To this end, the aforementioned fastening means can be formed by an outer screw thread on the outer face of the neck of the spout opening and a corresponding inner screw thread on the venting cover flange. Other fastening systems, such as for instance snap joints or clamp joints, can also be used.

Optionally, the vent opening in the venting cover is provided with a pop-off cap. To this end, the vent opening can be surrounded by a neck closely fitting into a peripheral flange of the pop-off cap, wherein the mutually facing sides of the neck and the flange are profiled to form a releasable snap joint. This profiling can include mutually cooperating beads and recesses as commonly used in the field of snap joint technology. This allows dimensioning of the snap joint in such a way that it will pop off at a certain pre-determined overpressure, e.g., a pressure in the range of 0.1 - 0.5 bar or higher, by selecting a material with suitable flexibility and optimizing the dimensions of the beads and the recesses.

The vent cover can for example have a diameter of 10 - 30 cm, e.g., about 15 cm. The pop-off cap can for example have a diameter of about 5 cm - 12 cm, e.g. about 7 cm. However, other dimensions for the venting cover and/or the pop-off cap, if present, may also be used, if so desired.

The containers of the present invention are particularly suitable for the storage and/or transport of compositions which are liable to exothermic decomposition, in particular peroxide formulations, optionally dissolved in phlegmatizers or in aqueous solutions, emulsions or suspensions. Generally, such containers can have a content of 600 - 1 ,400 litres, e.g. about 1 ,000 litres, although the content may be higher or lower, if so desired.

The venting cover of the invention can be mounted on any type of container known in the art. The containers can also be made of various types of materials,

such as metal containers, wooden containers, and composite or plastic containers.

In one embodiment of this invention, the venting cover is fitted on a container equipped with a special spring-loaded clamping strap for sealing by means of a lid, which clamping strap will release the lid at a certain level of super- atmospheric pressure in the container. Such containers are generally used for the transportation and storage of compounds or compositions liable to exothermic decomposition. This invention has the advantage of enabling the leak-tight transportation and/or storage of peroxides, and of preventing cracking or fragmentation of the container. Examples of this embodiment are disclosed in WO 95/26911.

In another embodiment, the venting cover is fitted on a container with at least one bursting area located above the liquid level in the container when the container is filled with such a liquid. The bursting area is defined as a weaker part of the container where, upon excessive pressure increase within the container, the bursting area will rupture first before the walls including the top and the bottom of the container do. The bursting area can be made of a material weaker than the material surrounding the bursting area or it can be made of the same material but weakened relative to the surrounding material. In one embodiment the bursting area is made thinner than its surroundings. The bursting area can have any shape and size as long as it is situated above the level of the liquid contained or to be contained in the container. In one embodiment, the bursting area coincides with the top side, which is made at least partially thinner than the bottom and the side walls. In one embodiment, the container comprises a venting cover in the top of the plastic inner container, which container is situated on a pallet and surrounded by a metal frame. The construction of the plastic inner container is such that at least part of the top side of the container is thinner than the bottom and the side walls. The bottom and the side walls of the plastic inner container are secured by the metal frame and the pallet-sized bottom construction, while the top side is less secured by a metal frame. At a certain level of superatmospheric pressure in the container, the venting cover will be opened first. If the pressure

rises further, the weaker top construction of the container will tear open in a controlled way. In this way a sufficient vent opening is created to release all gaseous decomposition products and no fragmentation or explosive rupture of the composite container will occur, allowing the liquid composition to remain in the container. In that embodiment these composite containers would, in principle, become suitable for the transport of several classes of liquid organic peroxide formulations and, although not preferred, other substances as mentioned in this patent application.

It is also envisaged to use containers with at least one bursting area as described above irrespective of the venting cover. In one embodiment, the invention pertains to a container containing a liquid composition liable to exothermic decomposition which comprises at least one bursting area above the level of the liquid composition. The container can be made of any material known in the art for such containers. Preferably, the container is made of a polymeric material such as polyethylene, for instance high density polyethylene (HDPE), polypropylene, and polyvinyl chloride. The polymeric material may further comprise additives which conduct electricity and which are capable of reducing any electrostatic energy on or in the vicinity of the container. In a preferred embodiment, the bursting area is made of the same material as used for the container. These bursting areas are preferably thinner than the material of the walls of the container.

These containers may comprise any venting cover known in the art including the venting cover described above. The invention also allows the venting cover to be absent.

The bursting area provides for a container which is safer and which can be made of materials such as plastics which would not normally be used for storage and/or transport of liquid compositions liable to exothermic decomposition, such as liquid peroxide formulations.

The invention is further illustrated by the drawings. In the drawings:

Figure 1 shows, partially in cross-section, a venting cover of a container according to the present invention; Figure 2 shows a side view of the container of Figure 1.

Figure 1 shows a part of a container 1 with a spout opening 2 with a peripheral neck 3 provided with an outer screw thread 4. A venting cover 5 comprises a body plate 6 to cover the spout opening 2. The body plate 6 of the venting cover 5 has a vent opening 7 which is covered by a pop-off cap 8. Along the periphery of the body plate 6, the venting cover 5 has a flange 9 with an inner screw thread 10 to cooperate with the outer screw thread 4 of the spout opening neck 3. A gas permeable sheet filter 11 of a perforated plastic foil material spans the spout opening 2 and is fixed between the screw connection 3, 4 between the spout opening neck 3 and the venting cover flange 9.

The pop-off cap 8 comprises a cap body 12 with a peripheral cap flange 13 capping a neck 14 surrounding the vent opening 7. The neck 14 is provided on its outside with a ridge or bead 15. The inner side of the cap flange 13 is provided with a ridge or bead 16 hooking past the neck's ridge 15 to form a releasable snap joint. The dimensions of the ridges 15, 16 and the elastic properties of the selected material are chosen such that the cap 8 pops off at a certain pre-determined overpressure.

Figure 2A is a side view of the container 1 , which can be placed on a pallet 17 comprising a support cage 18 of a steel grate construction, as shown in Figure 2B. The container 1 has a discharge opening 19 on its lower side. The venting cover 5 shown in Figure 1 is on top of the container 1. The container 1 can have a content of about 1 ,000 litres.