METHOD FOR MAKING A STERILE PRESSURE PACK

Abstract: A sterile pressure pack comprises a sealed pressure container (1) which contains a propellant gas and a pressurized product and has a discharge valve (3). Both the propellant gas and the product are introduced under pressure into the pressure container through the discharge valve. In a method for making the pressure pack, the pack is sterilized by heating the product, prior to said introduction, to such a high temperature, and by introducing the propellant gas and the product in such a time sequence, that the product, after said introduction, is sterilized itself and also sterilizes the propellant gas and the interior of the said pressure container.

Description: METHOD FOR MAKING A STERILE PRESSURE PACK The present invention relates generally to a method ,. for making a pressure pack comprising a sealed pressure container which contains a propellant gas and a pressur¬ ized product and has a discharge valve. 5 More particularly, the invention is concerned with a method for making such a sterile pressure pack. Demands on a higher shelf life for products within, for example, the drug and food industries have resulted . in an extensive use of preservatives. In recent years, 10 however, the possibilities of using preservatives have been reduced considerably, for which reason the packag¬ ing industry tried to switch to sterile packaging of the products. Present-day methods for the sterile packaging of 15 products are very time-consuming, complicated and there¬ fore expensive. Furthermore, their practising requires an extensive equipment. Prior art methods for the sterile packaging of products are basically of two types. 20 In the method of the first type, the entire packag¬ ing operation is conducted in a sterile space, use being made of a sterile container, a sterile propellant gas, and a product which has been sterilized beforehand. In a method of the second type, the actual filling 25 of the product and the propellant gas into the container is carried out first, whereupon the sealed container, with the propellant gas and the product contained therein, is heated to the requisite sterilization temperature for a period of time sufficient to sterilize the product, 30- the propellant gas and the container. q In one prior art method for sterile packaging of the type first above mentioned, the containers are first sterilized in some suitable manner and then filled with the product sterilized beforehand and fitted with valves also sterilized beforehand, before the sterile propellant in a final step is introduced automatically through the valve of the pack. In another method of the type first above mentioned, for the sterilization and filling of aerosol cans, an empty aerosol container provided with a valve is first sterilized and then filled with a sterile propellant gas and a liquid product sterilized beforehand. The many stages of the operation make these prior art methods unprofitable and necessitate extensive peripheral equipment. In addition many of these opera¬ tional stages are highly critical in that the sterility of the packaged product may be jeopardized if any of them should malfunction. One example of the prior art method of the second type mentioned above is the filling of a sterile product into an aerosol container. This technique may include, in a first stage, the cleaning of the open aerosol con¬ tainer with, for example, air, whereupon the product is introduced into the open container and a valve is fitted. After that, a propellant gas is usually supplied through the fitted valve, whereupon the aerosol can and its contents are heated for sterilization and leakage testing. In addition, a second long-term heating to high temperature is frequently carried out to ensure complete sterilization. After the second heating, the aerosol container is cooled and then is ready for storage. The requisite heating of the filled aerosol containers may take place in an autoclave or in a hot bath of, for example, oil, glycerol or some other indifferent solution. The heating is intended to impart to the con¬ tainers and their contents a temperature of, for example, 100-121°C during the requisite sterilization time which is, for example, at least 20 minutes. It is also known, as an alternative to sterilization of a filled pack by heating, to sterilize the filled pack by utilizing gamma or beta radiation in doses adapted to the size and contents of the pack. However, this sterilization technique ist not generally accepted and, furthermore, requires extensive machine equipment and safety measures against the radiation hazard. It therefore is the object of the present invention to provide a novel method for making a sterile pressure pack of the type mentioned by way of introduction, a method which is simpler and requires less complicated equipment than prior art methods. According to the invention, this object is achieved in that the pressure pack is sterilized by heating the product, prior to said introduction, to such a high temperature, and by introducing the propellant gas and the product in such a time sequence, that the product, after the said introduction, is sterilized itself and also sterilizes the propellant gas and the interior of the said pressure container. By heating the product prior to the introduction into the container, sterilization of the product proper can be initiated, or even fully completed, before the introduction. However, the final phase of the steriliza¬ tion of the product preferably occurs simultaneously with the sterilization of the container inside and of the propellant gas. The extent of the sterilization carried out before the product is introduced into the container depends on the product as such and on the construction of the filling equipment utilized. The contemplated sterilization of the product, the propellant gas and the container inside is achieved if the propellant gas is introduced before the product. However, the propellant gas may also be introduced imme¬ diately after the product, when the product temperature is still sufficiently high to enable sterilization also of the propellant gas. The propellant gas employed is a gas substantially insoluble in the product, and prefe- rably an inert gas, i.e. a gas which does not react chemically with the product. A substantially insoluble gas is preferred because the method according to the invention is intended primarily for pressure packaging of such products as are not in¬ tended to be discharged from the pressure container in aerosol form, but in a form in which the product is not mixed with the propellant gas. In other words, the propellant gas only is used for discharging the product and stays in the pressure container until substantially the entire product quantity therein has been discharged. In order to achieve complete sterilization with a minimum of product heating, the cooling of the pressure container after filling preferably should be delayed. To this end, the pressure container can either be heat- insulated or introduced into a hot medium, such as a heating tunnel or a heated liquid bath. For the same purpose, the pressure container may be heated before it is filled with the product. Finally, it may be suitable to change the position of the pressure container after it has been filled with the propellant gas and the product so that the product is repeatedly brought into contact with all of the inner surfaces of the container, thereby ensuring the requisite sterilization. The method according to the invention also affords the advantageous possibility that gas filling can be carried out in connection with the sealing of the con¬ tainer r and that product filling can be carried " out separately from the gas filling and the sealing in respect of both time and space r for example much later and in an entirely different location. To sum up, the characteristic features of the method according to the invention are as follows: the propellant gas is filled prior to or immediately after the product; a heated product is used to satisfy the sterilization requirement; filling is effected via the discharge valve; filling is carried out while the product is under pres¬ sure; filling is carried out with the container under normal atmospheric pressure; and an internal autoclaving occurs in the container after it has been filled with the propellant gas and the prod¬ uct. This means that the method according to the inven¬ tion brings the following advantages: 1. Rapid filling of the container, within a few se¬ conds. 2. No high-pressure chamber or bulky equipment is required. 3. Very short heating times, which is especially i - portant for delicate products. 4. Low power consumption. 5. The sealed containers are clean upon filling. 6. The filling of propellant gas can take place sepa¬ rately in time and space from the filling of the product. 7. The container is automatically tested for tightness during sterilization since the pressure within the container then considerably exceeds the pressure prevailing after the product has cooled. The invention will now be described in more detail below, reference being had to the accompanying drawing illustrating the different operational stages in a pre¬ ferred embodyment of the invention. In one embodiment of the invention, it is possible during filling and sealing of a container 1 in a first stage A to rinse the open can with, for example, nitrogen gas by means of a rinsing assembly 2, whereupon a valve 3 is fitted in a second stage B by means of a valve fitter 4, and in a third stage C propellant gas is supplied at a pressure of, for example, 1-2 atmospheres excess pressure through the valve 3 from a source 5 of pressure gas. In a forth stage D, a product heated to, for example, 130°C is supplied through the valve 3 from a pressure booster 6 via a product heater 7, whereupon the filled container 1 during a passive or retarded cooling period D in a heat-insulated or temperature-controlled chamber 8 is rotated to achieve complete sterilization of the container 1 and its contents which now have a temperature above the lowest practicable sterilization temperature, for example 100°C, during a predetermined minimum steri¬ lization period, for example 20 minutes. Upon termination of the sterilization period, the can may be cooled in a water bath for simultaneous leakage testing. The pressure increase is necessary to prevent the product from coming to the boil in the heater 7, but above all it is necessary for the rapid filling of the product into the container, during which the container 1 is under normal atmospheric pressure. In the method according to the invention, the heated product introduced into the container thus is used for in situ sterilization of the container inside, of the propellant gas, and of the product itself. It will be appreciated that there are obtained considerable advan¬ tages by such a far-reaching reduction in the number of process stages and in the complexity of the equipment employed. If the propellant gas is air, and if the air has been supplied at a pressure of, for example, 1-2 atmos¬ pheres excess pressure before the container is filled with the hot product, the container pressure may increase to, for example, 12-13 atmospheres excess pressure after the container has been filled with the hot product. During sterilization, i.e. the time during which the product temperature decreases to the minimum permissible sterilization temperature, the pressure within the con¬ tainer decreases, and after the final cooling, the pres- sure may be, for example, 10 atmospheres excess pressure. The container employed may have t e same form as an aerosol can and may be sealed hermetically by the fitting of, for example, a valve, lid or similar tight-fitting closure, or by fitting a lid or a closure comprising a non-return valve which is activated, i.e. closes, when the pressure within the container exceeds the atmos- pheric pressure. The container may by manufactured from any material which is capable of withstanding the pressures and tempe¬ ratures involved, and which is gas-tight. If the container is a metal container, the heat energy supplied by the product will, due to the heat conduction of the metal, spread to the entire pack which thus is automatically subjected to a uniform heat treatment. To ensure the uniform heating, it is possible, during the passive sterilization period, i.e. after the product has been filled into the container, to keep the pack in motion, for example by rotating or turning it so that all parts of the pack will be treated. The same technique can be used if the pack or the container is made of a mate¬ rial whose heat conductivity is inferior to that of metal, such as glass or plastic, in which case every part of the interior of the pack will be subjected to a similar heat treatment if the position of the container is changed for example by rotating or turning the con¬ tainer during the passive period of the treatment. To exemplify the invention, a test will now be described which was conducted with a conventional pressure container consisting of a monoblock of aluminium. The containers had a diameter of 40 mm and a total volume of 100 ml and were filled with air to an excess pressure of 0.5 atmospheres excess pressure before the containers where filled with liquid. The containers thus filled where allowed to cool in stationary ambient air of about 23°C. The "product" used for the 10-can test was tap 2 water which was supplied at a pressure of 7.0 kp/cm via a heating assembly which supplied the water at the temperature intended. The heating assembly consisted of a thermostat-controlled glycerol bath provided with a spiral tube of copper in which the water was heated. The hot water was supplied from the heating assembly through an insulated pressure hose to a special filling valve. When the valve was opened, the hot and pressu¬ rized water spouted directly into the container via the discharge valve thereof. In this manner, the container, its seal and valve and also the air within the container were heated by the superheated water supplied. By setting the superheating temperature in relation to the bulk of the supplied liquid and the bulk and the initial temperature of the can, the metal wall of the can was heated to a temperature above the lowest practical steri¬ lization temperature, in this case about 120°C, and was held above this temperature during the cooling. In the test accounted for in the Table below, the temperature of the metal wall of the can is measured by means of a thermocouple whose probe was clamped against the metal wall by means of a thoroughly heat-insulated clamp. The first temperature measurement was made immedia¬ tely after the can had been filled to the intended degree of filling, i.e. 75%, whereupon the temperature of the can wall was measured every minute for 20 minutes. The test results are shown in Table 1. It appears from the table that the can temperature could be maintained above the minimum sterilization temperature by superheating the "product" prior to filling so that complete steri¬ lization could be achieved without any special steriliza¬ tion measures. In this case, the cans where allowed to cool in stationary air of room temperature, but if longer or shorter sterilization periods are desired, ambient conditions during cooling may be changed so that cooling will be slower or quicker. Although the test was conducted with tap water, the technique is, of course applicable to any liquid or semiliquid product. However, it is intended primarily for aqueous products. TABLE 1 Temperature of water supplied, 195°C Aerosol can, 40 mm. Total volume 100 ml. Fill-up volume 75 ml. Excess pressure in can prior to filling, 0.5 at . above atm. pressure Ambient temperature ~ 23°C (stationary air) o ■ H P Can H Minutes after filling No - Filled-up quantity 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 of hot water (g) 1 160 157 155 153 150 148 146 144 142140 138 136 134 132131 129 127 125124 122 121 75.5 2 161158 155 152 150147 145143 141139 137 135133 131 129 127 125123122121120 75.0 3 164 160 158 156 153 151149 157 145143 141139 137 135 133 131129 127 125 123 122 76.5 4 158 155 153 150 148 146 144 142 140 138 136 134 132 130 128 127 125 124 122 121 120 74.0 5 159 157 154 152 150 148 146 144 142 140 138 137 135 134 132 130 128 126 125 123 112 74.5 6 162 159 156 154 159 150 147 145 143 141 139 137 134 131 130 128 126 125123 122 120 76.0 7 166 162 159 156 153 151 148 146 144 142 140 138 136 134 133 131 130 128 126 125124 78.0 8 159 156 153 151 149 147 145 143 141139 137 135 133 131 130 128 126 125123 121 120 73.0 9 164 161 158 155 153 151 149 147 145 143 141 138 136 134 132 130 128 127 125 124 123 77.5 10 163 160 157 154 152 150 148 146 144 142 140 138 135 133 131 129 127 126 124 123 121 75.5

Claims: CLAIMS 1. Method for making a sterile pressure pack compri¬ sing a sealed pressure container which contains a propel¬ lant gas and a pressurized product and has a discharge valve, in which method both the propellant gas and the pressurized product are introduced into the pressure pack via said discharge valve, c h_ a r a c t e r i z e d in that the pressure pack is sterilized by heating the product, prior to said introduction, to such a high temperature, and by introducing the propellant gas and the product in such a time sequence, that the product, after the said introduction, is sterilized itself and also sterilizes the propellant gas and the interior of the said pressure container. 2. Method as claimed in claim 1, c h a r a c t e - r i z e d in that the propellant gas employed is a gas substantially insoluble in the product. 3. Method as claimed in claim 1 or 2, c h a r a c ¬ e r i z e d in that the propellant gas employed is an inert gas. 4. Method as claimed in any one of claims 1-3, c h a r a c t e r i z e d in that the propellant gas is introduced before the product. 5_ Method as claimed in any one of claims 1-4, c h a r a c t e r i z e d in that cooling of the pressure container is delayed after filling of the product. 6. Method as claimed in claim 5, c h a r a c ¬ t e r i z e d in that the pressure container is heat- insulated or introduced into a hot medium after filling of the product. 7. Method as claimed in any one of claims 1-6, c h a r a c t e r i z e d in that gas filling is carried out in connection with the sealing of the container and separately from the product filling. 8. Method as claimed in any one of claims 1-7, c h a r a c t e r i z e d in that the pressure container is heated before filling of the product. 9. Method as claimed in any one of claims 1-8, c h a r a c t e r i z e d in that the position of the pressure container is changed after filling of the pro¬ pellant gas and the product.

Inventors: LOODBERG JAN AAKE TORSTEN, LOODBERG, JAN, AAKE, TORSTEN
Applicants: CIKAB AB, AB CIKAB
Application year: 1987
Main classification: B65B55
IPC codes: A61L2, B65B31, B65B55