Improvements of the hydrophobic properties of the tilting valve grommet of an aerosol can

0001The present invention concerns an improvement to a rubber grommet for a tilting and/or gun aerosol valve grommet (hereafter called the aerosol valve grommet), more particularly regarding the protection against moisture diffusion and uptake through the rubber grommet.

0002Generally the aerosol valve will be used for dispensing one or two component polyurethane (PU) foam systems contained in a pressurized can or vessel or any other polymer system curing or sensitive by/to moisture/water uptake.

0003The type of aerosol valves relevant for the present invention is used for more than 25 years in order to dispense the content of an aerosol can. By tilting or vertical activation of the stem, the valve opens and delivers the vessel's content. Such a valve consists of a number of plastic and metal parts. The inner gasket/seal, called the grommet, is made of rubber. Other parts are a special metal cup with inlaid rubber gasket and a plastic stem.

0004Since the chemical components present in the can or vessel are water sensitive and react with water to form for example the final polyurea in the case of a polyurethane prepolymer , it should be acknowledged that any contact with ambient moisture is to be avoided in order to prevent the forming of polyurethane and/or similar derivatives inside the can or vessel. Moisture penetrates via the valve system, more particularly through the grommet in the case of aerosol valves.

0005The polyurethane and/or similar components formed due to moisture uptake (diffusion) inside the can or vessel sticks against the grommet and or the stem. Once the first layer of PU formed on the grommet on the face inside the can or vessel, the sealing properties of the valve diminished and makes the valve subject to blocking and/or leaking.

0006A standard tilting or gun valve get stucked after contact with the polyurethane prepolymer in the can at higher temperature and higher conditions of humidity. This contact is made possible by inappropriate storage of cans (horizontal or upside down) or excessive shaking during transport.

0007It is believed that the stucking/blocking of the valve is made possible by a combination of at least two features <ul id="ul0001" list-style="dash" compact="compact"><li>water diffusion through the grommet from the outside to the inside of the aerosol can or vessel,</li><li>diffusion of prepolymer through the grommet from the inside of the can with the propellant as carrier.</li></ul>

0008Where both water and prepolymer are meeting a reaction will take place and a kind of cylindrical hardness front will be formed. This hardness front will prevent the stem from being tilted or displace vertically and will result in a stucked valve.

0009Therefore there is a need for an improved appropriate moisture repulsive grommet.

0010In order to prevent moisture uptake through the grommet, a hydrophobic thermoplastic or non thermoplastic elastomer could be used such as : styrene-butadiene, butylene-styrene, silicone rubbers, isopropyl ether (Kraton, Shell), chlorinated polyethylene (Tyrin, Dupont de Nemours), epichlorhydrin homopolymers or copolymer, ethylene propylene (Nordel, Dupont de Nemours), fluoroelastomers (Viton, Dupont de Nemours), alcryn MPR (chlorinated olefin interpolymer alloy), Santoprene etc..

0011According to the present invention, there is a provided a rubber grommet with a moisture barrier provided by chemical treatment of a rubber grommet that may be otherwise usual. The rubber can be BUNA, EPDM or Neoprene, butyl etc...

0012The chemical treatment is a coating of at least part of the grommet surface in contact with the container's component, by a inert hydrophobic substance dispensed or brushed on said surface or by dipping or impregnation of the whole grommet into the substance.

0013The invention will be better understood with reference to the annexed figures provided as examples.

0014Fig. 1 illustrates an example of the tilting of a valve as is well-known, with the grommet 1, the stem 4 and the cup 5 to be coupled with the aerosol can or vessel (not illustrated). The tilting action provides an open passageway for the content of the can.

0015Fig. 2 illustrates a similar valve, the arrows indicating the diffusion of the propellant and prepolymer from the inside of the can on one side and, on the other side, of the moisture from the environment. It is to be noted that the moisture may access the grommet also through the hollow stem. There is shown an internal "front" in the grommet where a reaction between both components occurs and wherein consequently hardness is increased.

0016Fig. 3 represents schematically a transversal section of an isolated classical grommet 1 with a hole 2 for the stem and for which the bottom part 3 has been coated according to the invention, for example by spraying (arrows), brushing, dipping or impregnation of the whole grommet.

0017The chemicals used for this type of application are preferably silicon or fluoro-polymer based compositions.

0018According to the invention, the treatment may be conducted either by spraying or directly laying a coating by dipping or impregnation of the whole grommet. For example, preferably just after demoulding the rubber, it can be sprayed by a coating/reactive agent. The rubber can also be brushed, impregnated or plasma treated in order to obtain a coating on the whole surface of the grommet or only on the bottom part (ref. 3 in fig. 1). The applied composition can be a solution of fluoro-polymer or a silicon based composition.

0019It has been found that a silicon based composition for coating or impregnation of the ACMOS type is appropriate, for example ACMOS 70-2406. The Münch coating spray MKX 02-125 may also be used. It is postulated that some chemical (covalent) bonding is produced between the coating and the rubber.

0020After the coating, impregnation or plasma treatment, the grommet is siliconized. This extra post siliconisation improves the snappiness of the rubber and the multi-use properties of the valve. A typical silicone mixture used is Bayer M350.

0021A significant improvement in overall properties of the valve is noticed. In a test, the aerosols or vessels are stored vertically, horizontally and shaken every day, which represent critical situations for a valve. It has however been found that the valves treated according to the invention are still working and no leakage or blocking of the can or vessel is encountered.