Method for sterilizing the blowing network of a thermoplastic container molding machine

Abstract

The present invention relates to a method for sterilizing a container forming machine comprising an injection network and a sterilization device, the sterilization device comprising a source of dry gas, a source of sterilizing steam and a chamber for mixing the sterilizing steam with the dry gas to form a sterilizing gas mixture, the method comprising a step (E1) of heating a duct of the injection network by injecting hot dry gas and a second step (E2) of injecting the sterilizing gas mixture into the injection network, characterized in that the second step (E2) is initiated when the coldest point of the injection network reaches a processing temperature (Ti) that is higher than the condensation temperature (Td) of the sterilizing steam and lower than the temperature (Tg) of the drying gas.

Description

Technical Field

[0001] The present invention relates to a method for sterilizing a molding machine for molding a container from a thermoplastic preform, the molding machine comprising a blowing network having a duct connecting a controlled source of compressed blowing gas to at least one blowing nozzle for molding the container by blowing, the molding machine comprising a sterilization device for the blowing network, the device comprising a controlled source of pressurized hot dry gas, different from the controlled source of blowing gas, a source connected to the blowing network at a supply junction, and a controlled source of sterilizing steam containing vaporized oxidant, and a chamber for mixing the sterilizing steam with the dry gas to form a sterilizing gas mixture containing vaporized oxidant and water vapor, and comprising The method comprises heating the ducts of the blowing network only by injecting pressurized hot dry gas, during which the dry gas heats the inner walls of the ducts of the blowing network, and a second step of injecting a sterilizing gas mixture into the blowing network, and comprising

Background Art

[0002] To do this, the container manufacturing equipment comprises at least one oven for heating a preform associated with a molding machine (also called a "blowing machine") for molding the container from the hot preform. The equipment also advantageously comprises a sterilization unit for sterilizing at least the interior of the preform so as to obtain a so-called "sterilized" container.

[0003] To form a preform by blowing or stretch-blowing, it is known that in one or more steps, at least one fluid, generally a gas, such as compressed air at a pressure of up to 30 or 40 bar depending on the application, is used for blowing. To allow for a more uniform distribution of the material in the final vessel, there is often a preliminary pre-blowing operation, which consists of injecting a blowing fluid at a lower pressure, for example, 13 bar, into the preform before proceeding with the actual blowing operation with the high-pressure blowing gas as described above.

[0004] The air used for blowing is introduced into a heated preform placed within the mold so that the blown air comes into direct contact with the inner surface of the container. For this purpose, the molding machine is equipped with a controlled source of blown air that supplies it to multiple blown nozzles via a blown duct.

[0005] Here, the inner surface itself is intended to subsequently come into contact with the product that will be packaged in the container.

[0006] Therefore, the quality of the infused air, more specifically the absence of contaminants such as microorganisms and particles such as dust, is an important parameter that should be considered in the overall control of the risk of contamination of the containers being manufactured, especially in the case of packaging in the food industry, in order to ensure the good preservation of packaged products, particularly their shelf life, and consumer safety.

[0007] Here, the quality of the compressed air used for blowing is determined by a range of factors, from the quality of the inhaled air, which varies depending on the environment of the industrial site relative to the pollution source and its location, to the condition of the distribution network and / or equipment.

[0008] The air drawn in and compressed by at least one compressor exhibits, for example, more or less relative humidity, and moisture promotes corrosion and the growth of microorganisms.

[0009] Particular attention is paid to the selection of compressors, as their design, and more specifically, their lubrication methods, can easily cause chemical contamination of the air by, for example, lubricating oil or even Teflon® dust.

[0010] This is why compressed air intended for use in blowing is pre-treated, and more specifically, filtered by gas filtration means to obtain "sterile" air, i.e., air free of microorganisms in particular, for blowing.

[0011] The compressed air used for injection is generally continuously filtered by a filtration system equipped with different gas filtration means.

[0012] In a non-limiting embodiment, such a system for filtering air intended for blowing comprises, for example, a plurality of filtering means arranged in series, the plurality of filtering means intended to deliver sterile air at the output.

[0013] The air inside is continuously filtered by a first filtration means of type "FFP" to obtain, for example, oil removal, water purification, and dust removal; then filtered by a second filtration means of type "AK" (activated carbon) to remove all oil and gaseous hydrocarbon vapors that may also cause unpleasant odors or tastes; and finally filtered by a third filtration means of type "SRF" to retain microorganisms.

[0014] In fact, the blown air is likely to become a vector for contamination of the inside of the preform and therefore the container by introducing contaminants, more specifically microorganisms (viruses, bacteria, spores, etc.), into it.

[0015] In container manufacturing methods, if the container filling is performed in a sterile environment immediately after molding of the container obtained by hot preform blowing or stretch blowing, controlling the quality of the compressed air used for blowing becomes even more important.

[0016] In fact, in such manufacturing methods, sterilization is generally performed upstream of the preform before conversion to containers, and as a result, it is essential to prevent the risk of contamination of the sterilized preform, such as the containers manufactured from these preforms.

[0017] The present invention aims to sterilize the blowing duct, which is located downstream of the filtration means and leads sterile blown air to the blowing nozzle. This makes it possible to ensure that the air remains sterile until it reaches the preform.

[0018] Sterilization of the blowing duct must enable the destruction of any existing microorganisms in order to prevent outbreaks within the blowing duct and thus eliminate the risk of preform contamination.

[0019] For industrial applications such as the manufacture of containers for packaging food products, it is crucial to be able to guarantee the quality, and more specifically, the sterility, of the blown air.

[0020] To sterilize the blowing duct, it is known to circulate a sterilization gas mixture containing a gaseous oxidizing agent within the blowing duct. The gaseous oxidizing agent is generally formed by the evaporation of a liquid oxidizing agent, such as hydrogen peroxide (H2O2).

[0021] Such sterilization gas mixtures have the disadvantage of condensing on the inner walls of the blowing ducts. Contact with an oxidizing agent in the gas phase allows for the elimination of microorganisms without damaging the blowing ducts. However, given the strong oxidizing power of the oxidizing agent, condensed droplets containing the oxidizing agent rapidly damage the inner walls of the ducts through corrosion.

[0022] To solve this problem, it is known that the blowing ducts can be manufactured from stainless steel. However, such materials are very expensive, which greatly increases the manufacturing cost of the molding machine. [Overview of the project] [Problems that the invention aims to solve]

[0023] Therefore, the present invention proposes a solution that enables the avoidance of the occurrence of oxidant condensation during the sterilization operation. This makes it possible, in particular, to use less expensive metallic materials in the manufacture of the blowing ducts.

Means for Solving the Problem

[0024] The present invention relates to a method for sterilizing a molding machine for molding a container from a thermoplastic preform. The molding machine comprises a blowing network having a duct connecting a controlled source of compressed blowing gas to at least one blowing nozzle for molding the container by blowing, and the molding machine comprises a device for sterilizing the blowing network, the device comprising a controlled source of pressurized hot dry gas, different from the controlled source of blowing gas, connected to the blowing network at a supply junction, and a controlled source of sterilizing steam containing vaporized oxidant, and a chamber for mixing the sterilizing steam with the dry gas to form a sterilizing gas mixture containing vaporized oxidant and water vapor, and comprising The method comprises heating the ducts of the blowing network only by injecting pressurized hot dry gas, during which the dry gas heats the inner walls of the ducts of the blowing network, a second step of injecting a sterilizing gas mixture into the blowing network, and comprising The second step of injecting the sterilizing gas mixture is started when the coldest point, called the cold point, of the blowing network exposed to the sterilizing gas mixture reaches a treatment temperature higher than the condensation temperature of the water vapor and the vaporized sterilizing agent at the cold point, the treatment temperature being lower than the temperature of the hot dry gas obtained at the supply junction.

[0025] According to another feature of the method carried out in accordance with the teachings of the present invention, the processing temperature is determined such that the ratio of the partial pressure of the mixture of water vapor and vaporized sterilizer at the low point of the blowing network to the saturated vapor pressure of the mixture, called the relative saturation, is within a determined range of 70% to 90%.

[0026] According to another feature of the method implemented in accordance with the teachings of the present invention, the determined range is 80% to 90%.

[0027] According to another feature of the method carried out in accordance with the teachings of the present invention, the processing temperature is measured by a probe placed at a low temperature point.

[0028] According to another feature of the method carried out in accordance with the teachings of the present invention, the relative saturation is measured by a sensor at the low temperature point of the injection network.

[0029] According to another feature of the method implemented in accordance with the teachings of the present invention, the temperature, humidity, and pressure of the dry gas at the supply joint are constant.

[0030] According to another feature of the method implemented in accordance with the teachings of the present invention, a controlled supply source of drying gas is controlled at a constant flow rate throughout the entire duration of the sterilization method.

[0031] According to a first embodiment of a method carried out in accordance with the teachings of the present invention, a controlled source of sterilization steam is controlled at a constant flow rate during a second step of injecting a sterilization gas mixture of the sterilization method.

[0032] According to a second embodiment of a method carried out in accordance with the teachings of the present invention, a controlled supply source of sterilization steam has a flow rate that can occupy at least one intermediate flow rate between zero flow rate and maximum flow rate throughout the sterilization method.

[0033] According to another feature of the method carried out in accordance with the teachings of the present invention, the flow rate of sterilization steam in the mixing chamber is controlled according to measurements made by a sensor to keep the relative saturation at the low temperature within a determined range.

[0034] The present invention also relates to a molding machine for carrying out a method performed in accordance with the teachings of the present invention, the molding machine comprising a blowing network comprising a duct connecting a controlled source of compressed blowing gas to at least one blowing nozzle for forming a container by blowing, the molding machine comprising a device for sterilizing the blowing network, the device is A controlled supply source of pressurized high-temperature dry gas, which differs from a controlled supply source of blown gas, and is connected to a blown network at the supply junction, A controlled source of sterilization steam containing vaporized oxidizing agent, A chamber for mixing sterilization vapor with a dry gas to form a sterilization gas mixture containing vaporized oxidizing agent and water vapor, Equipped with, The system is characterized by comprising a temperature probe positioned to measure the temperature inside the nozzle or in the duct of the blowing network adjacent to the nozzle.

[0035] Other features and advantages of the present invention will become apparent upon reading the detailed description below. Refer to the accompanying drawings for further understanding. [Brief explanation of the drawing]

[0036] [Figure 1] This is a pneumatic diagram representing a molding machine for carrying out a method performed according to the teachings of the present invention. [Figure 2] This is a pneumatic diagram showing in more detail one of the molding stations where the molding machine shown in Figure 1 is located. [Figure 3] This is a pneumatic diagram showing in more detail the sterilization apparatus in which the molding machine shown in Figure 1 is installed. [Figure 4] This block diagram shows a sterilization method performed by a first embodiment of the present invention that realizes the molding machine shown in Figure 1. [Figure 5] Figure 1 shows the temperature within the injection network of the molding machine as a function of the length of the duct extending from the supply connection point with the sterilization device towards the nozzle. [Figure 6] This figure shows the trend of the relative saturation of the gas present at the low temperature point of the injection network of the molding machine shown in Figure 1, as a function of time during the implementation of the method shown in Figure 4. [Figure 7] This block diagram shows a sterilization method according to a second embodiment of the present invention that realizes the molding machine shown in Figure 1. [Modes for carrying out the invention]

[0037] In the following description, elements having the same structure or similar function are indicated by the same reference numeral.

[0038] In the following explanation, the terms “upstream” and “downstream” are used to describe the direction of gas flow within the duct.

[0039] Figure 1 is a pneumatic diagram showing an exemplary embodiment of a machine 10 for forming a container by blowing or stretch-blowing a preform made of a thermoplastic material.

[0040] The molding machine 10 has a part 12 fixed to the ground and a rotating part 14 attached to a rotating carousel (not shown).

[0041] The rotating section 14 comprises a plurality of molding stations 16 mounted on a carousel. This arrangement allows for the mass production of containers. As shown in Figure 2, each molding station 16 comprises a mold 18 having a die for the container to be manufactured, intended to contain a preform. Each molding station 16 also comprises an injection nozzle 20 adapted to blow pressurized molding gas into the preform contained in the mold 18. This is, for example, a nozzle 20 with a dome-shaped end fitting 22 intended to cap the neck portion of the preform contained in the mold 18.

[0042] The fixed section 12 includes a controlled supply source 24 of compressed blown gas. The blown gas is compressed to, for example, about 40 bar. The blown gas is, for example, air.

[0043] A controlled supply source 24 of the blown gas is connected to the nozzles 20 of each molding station 16 by a network of blown ducts, which are hereafter referred to as the blown network 26 in this specification and in the claims. The ducts of the blown network 26 are hereby made of a material that is readily oxidized upon contact with an oxidizing agent in liquid form, such as hydrogen peroxide or acetic acid, unlike ducts made of stainless steel material.

[0044] More specifically, the injection network 26 includes a main supply duct 28 connecting a controlled supply source 24 of injection gas to a rotary joint 30, thereby enabling the formation of an interface between the fixed part 12 and the rotating part 14. The injection network 26 also includes at least one distribution ramp 32 belonging to the rotating part 14 and connected to the main supply duct 28 via the rotary joint 30. The distribution ramp 32 is connected to each of the molding stations 16 by an associated distribution duct 34.

[0045] To ensure the quality of the blown air, a filtration component 35, such as an "SRF" type filter, is inserted into the main supply duct 28.

[0046] As shown in Figure 2, in each of the molding stations 16, the injection network 26 also includes a high-pressure injection duct 36 connected to a distribution duct 34 associated with the nozzle 20. A two-way injection valve 38 is inserted into the high-pressure injection duct 36. The injection valve 38 is controlled alternately between an open position and a closed position.

[0047] At each of the molding stations 16, the injection network 26 also includes a low-pressure pre-injection duct 40, which connects a distribution duct 34 associated with the nozzle 20 in parallel with the high-pressure injection duct 36. The low-pressure injection duct 40 includes an injection gas pressure regulating member 42 to reduce the pressure to, for example, about 13 bar. A two-way pre-injection valve 44 is inserted into the low-pressure injection duct 40. The pre-injection valve 44 is controlled alternately between an open position and a closed position.

[0048] The molding machine 10 also includes a device 46 for sterilizing the blowing network 26. The sterilization device 46 includes a controlled supply source 48 of pressurized thermal drying gas, such as air. The controlled supply source 48 of the drying gas is separate from the controlled supply source 24 of the blowing gas. The controlled supply source 48 of the drying gas is connected to the blowing network 26 via a sterilization duct 50 at a supply joint 49.

[0049] A controlled supply source 48 of the dry gas is located here in the fixed section 12 of the molding machine 10. A supply joint 49 is also located in the fixed section 12 of the molding machine 10, preferably upstream of the rotary joint 30. The supply joint 49 is located here in the main blowing duct 28. More specifically, the supply joint 49 is located upstream of the filtration member 35.

[0050] In modified versions of the present invention not shown, the supply connection is positioned close to the downstream of the filtration member. In this case, it is preferable to provide the sterilization member with additional sterilization means.

[0051] The sterilization apparatus 46 is shown in detail in Figure 3. The controlled supply source 48 of the drying gas includes a supply source 52 of pressurized gas, such as air, to supply to the sterilization duct 50. The controlled supply source 48 of the drying gas further includes a filter 54 to ensure that the drying gas is free of impurities, a pressure regulating member 56, and a member 58 for heating the drying gas to a predetermined temperature. The temperature "Tg" of the hot air drying gas is, for example, about 180°C. The controlled supply source 48 of the drying gas further includes a valve 60 for adjusting the flow rate of the drying gas. The adjustment valve 60 is controlled to be either in a closed position where the flow rate of the drying gas is zero, or in an open position where the drying gas is supplied at a constant flow rate.

[0052] The sterilization apparatus 46 also includes a controlled supply source 62 of sterilization steam. As shown in Figure 3, it includes a tank 64 of sterilization solution containing an oxidizing agent. The oxidizing agent is, for example, hydrogen peroxide (H2O2) or peracetic acid. The sterilization solution is formed, for example, from an aqueous solution containing a determined concentration of the oxidizing agent, for example, a solution of hydrogen peroxide diluted to 25% in water.

[0053] The controlled source of sterilization steam 62 also includes an evaporator 66 in which sterilization steam is generated by the total evaporation of the sterilization liquid supplied by the sterilization liquid tank 64 via an injection duct 68. The evaporator 66 includes a heating element 69 that heats to a temperature sufficient to allow instantaneous evaporation of the sterilization liquid. The heating element 69 is located within the chamber of the evaporator 66. Thus, the sterilization steam contains vaporized oxidizing agent and water vapor in clearly defined proportions.

[0054] The controlled supply source 62 of sterilization steam further comprises a device 72 for distributing the sterilization solution, which is inserted between the sterilization solution tank 64 and the evaporator 66. Herein, the distributor 72 has an adjustable flow rate.

[0055] The chamber of the evaporator 66 here forms a chamber 70, which is for mixing sterilization vapor with a dry gas to form a sterilization gas mixture exhibiting a partial sterilization vapor pressure determined as a function of the mass flow rate of the dry gas and the mass flow rate of the sterilization vapor. For this purpose, the mixing chamber 70 is inserted into the sterilization duct 50.

[0056] Since the mixing chamber 70 is directly formed here by the chamber of the evaporator 66, the mass flow rate of the sterilization vapor is understood to be the mass of sterilization vapor produced per unit time by evaporation in the evaporator 66.

[0057] In variations not shown, the mixing chamber is separate from the evaporator chamber. The mixing chamber is then positioned downstream of the evaporator in the direction of the sterile steam flow.

[0058] The sterilization device 46 also includes a flow control valve 74 inserted into the sterilization duct 50 downstream of the mixing chamber 70. The control valve 74 is controlled to either a closed position, which prohibits the passage of gas into the blowing network 26, or an open position.

[0059] The molding machine 10 can operate according to a manufacturing mode in which the sterilization device 46 is controlled so as not to send sterilization steam or drying gas to the blowing network 26. In manufacturing mode, a controlled supply source 24 of the blowing gas is controlled to inject the blowing gas into the blowing network 26. The blowing valves 38 and auxiliary blowing valves 44 of each molding station 16 are controlled according to the position of the molding station 16 relative to the fixed part 12, and alternately blow gas at low pressure and then at high pressure to enable the molding of the container from the preform.

[0060] The molding machine 10 can also operate according to a sterilization mode, which can only be performed when the manufacturing mode is stopped. The sterilization mode is activated, for example, when the container format is changed and / or even at regular time intervals, to avoid the growth of bacteria in the blowing network 26. Generally, the sterilization mode is favorably activated before the molding machine 10 is set to manufacturing mode. When the sterilization mode is performed, the mold is empty, i.e., does not contain a preform.

[0061] When operating in sterilization mode, the molding machine 10 performs the sterilization method shown in Figure 4.

[0062] In the following, the condensation temperature "Td" of a mixture of water vapor and vaporized sterilizer is defined as the temperature at which water vapor and / or vaporized sterilizer begin to condense, for a determined molar concentration of each and a determined total pressure of the sterilization gas mixture. The condensation temperature "Td" is determined, for example, by a phase diagram or chart showing the condensation temperature "Td" as a function of pressure and / or as a function of the molar concentration of vaporized sterilizer in the sterilization gas mixture. This parameter is generally given by the sterilizer supplier at the time of product delivery. This parameter can also be found in or easily estimated from studies well known to those skilled in the art, such as Schumb et al.'s "Hydrogen Peroxide" in 1955.

[0063] The partial pressure of vaporized sterilizer in a sterilization gas mixture is also defined as the pressure possessed solely by the vaporized sterilizer. This partial pressure is particularly dependent on the ambient temperature and the molar concentration of vaporized sterilizer present in the sterilization gas mixture.

[0064] Similarly, the partial pressure of water vapor in a sterilization gas mixture is also defined as the pressure possessed solely by water vapor. This partial pressure is particularly dependent on the ambient temperature and the molar concentration of water vapor present in the sterilization gas mixture.

[0065] Molar concentration can be defined from the weight or volume concentration of the sterilizer. This allows us to determine the molar concentration of the sterilizer in vapor form within the sterilization gas mixture by knowing the mass flow rate of the sterilization steam and the mass flow rate of the drying gas.

[0066] Saturated vapor pressure is also defined as the partial pressure of the gaseous component in the sterilization gas mixture at which the component begins to condense. Saturated vapor pressure increases with ambient temperature. Therefore, in a high-temperature atmosphere, the sterilization gas mixture may contain a higher concentration of the gaseous component before reaching saturated vapor pressure, compared to a lower-temperature atmosphere, under the same pressure conditions.

[0067] The relative saturation degree "RS" of a sterilization gas mixture is defined as the ratio of the sum of the partial pressures of the sterilizer and water vapor in vapor state to the saturated vapor pressure of the water vapor and vaporized oxidizing agent in the sterilization gas mixture. The relative saturation degree "RS" is expressed here as a percentage and the temperature conditions are defined. Therefore, as long as the relative saturation degree "RS" is less than 100%, no condensation will occur in the sterilization gas mixture. When the relative saturation degree "RS" reaches 100%, water and / or the oxidizing agent begin to condense. The relative saturation degree "RS" of a mixture of vaporized sterilizer and water vapor is determined by a phase diagram or chart that shows the relative saturation degree "RS" as a function of pressure, and / or as a function of ambient temperature, and / or as a function of the molar concentration of vaporized sterilizer in the sterilization gas mixture.

[0068] Finally, the relative humidity of a dry gas is defined as the partial pressure of water vapor in the dry gas relative to the saturated vapor pressure of water vapor.

[0069] In the method carried out according to the teachings of the present invention, several parameters such as temperature "Tg", relative humidity, and the pressure of the dry gas at the supply joint 49 remain constant throughout the sterilization method. The flow rate of the controlled supply source 48 of the dry gas also remains constant at all steps of the sterilization method.

[0070] Before initiating the sterilization method, a set value for the sterilization steam flow rate is determined to ensure thorough sterilization of the blowing network 26. The flow rate set value is, for example, approximately 0.19 kg / h for a molding machine 10 with 6 stations and approximately 1.9 kg / h for a molding machine 10 with 30 stations. This set value is, for example, a function of the length of the blowing network 26. The time "d" that the blowing network 26 is exposed to the sterilization gas mixture is also determined. The duration of the sterilization method is, for example, approximately 30 minutes, with each of the three steps lasting approximately 10 minutes, as described below.

[0071] According to the first embodiment of the sterilization method, the set value of the sterilization steam flow rate and the exposure time "d" are predetermined. These are constant values ​​determined by experiment or calculation according to the characteristics of the molding machine 10, such as the number of molding stations 16.

[0072] On the other hand, the method according to the present invention proposes acting on the temperature of the blowing network 26 in order to avoid condensation of sterilization steam in the duct of the blowing network 26.

[0073] To enable sterilization of all ducts in the blowing network 26, the blowing valve 38 and the auxiliary blowing valve 44 are kept open throughout the entire duration of the sterilization method, as shown in Figure 2. The controlled supply source 24 of the blowing gas is controlled to the closed position throughout the entire duration of the sterilization method.

[0074] This method includes a first step "E1" in which the ducts of the injection network 26 are heated. In this first step "E1", only pressurized high-temperature dry gas is injected into the injection network 26 at a determined flow rate. Thus, the dry gas flows in one direction from the supply joint 49 to the nozzle 20, heating each duct of the injection network 26 to at least the processing temperature "Ti".

[0075] This method also includes a second step "E2" of injecting a sterilization gas mixture into the injection duct, which is triggered at the end of the first heating step "E1". A device 72 for distributing the sterilization solution is controlled to inject the sterilization solution at a flow rate corresponding to a set value for the sterilization vapor flow rate. During this step "E2" of injecting the sterilization gas mixture, the vaporized oxidizer present in the sterilization gas mixture sterilizes the duct of the injection network 26 by direct contact. The sterilization gas mixture flows in one direction from the supply joint 49 to the nozzle 20. A sterilization gas mixture suction duct (not shown) is provided, located downstream of the nozzle 20, or adjacent to the end fitting 22, or connected to the nozzle in the mold, to allow the sterilization gas mixture containing the sterilizer to be exhausted after passing through the injection network 26.

[0076] Finally, as indicated by condition "C3", when the aeration time "d" is reached, the third and final aeration step "E3" is triggered. The device 72 for distributing the sterilizing solution is then closed to stop the generation of sterilizing vapor. Meanwhile, the flow rate of the drying gas is maintained. Thus, the drying gas continues to circulate in the duct of the blowing network 26 for the time required to discharge the residue of the sterilizing vapor. The process then ends as indicated by symbol "S2".

[0077] The purpose of the first heating step "E1" is to heat the duct of the blowing network 26, that is, the inner wall forming the duct, to a processing temperature "Ti" that is higher than the condensation temperature "Td", in order to ensure that sterilization steam does not condense when it comes into contact with the duct of the blowing network 26.

[0078] The second step "E2" of injecting the sterilization gas mixture is triggered before all the ducts of the blowing network 26 are heated uniformly. Because they are not heated uniformly at the start of the method, the blowing network 26 has a portion of the duct that is colder than the rest of the ducts of the blowing network 26, which is called the "cold point 75". More specifically, the second step "E2" of injecting the sterilization gas mixture is triggered when the cold point 75 of the blowing network 26 exposed to the sterilization gas mixture reaches a processing temperature "Ti" that is lower than the temperature "Tg" of the hot dry gas taken at the supply joint 49.

[0079] This low-temperature point 75 is generally located within the nozzle 20, or in close proximity to the nozzle 20, for example, just upstream of the nozzle 20, or downstream of the nozzle 20 in the mold 18. In fact, the duct of the injection network 26 is cooler than the processing temperature "Ti" at the start of the method. In its flow within the duct of the injection network 26, the hot drying gas, as a matter of priority, first exchanges heat with the duct of the injection network 26 located in close proximity to the supply joint 49, thereby establishing a temperature gradient that decreases as a function of the length "L" of the duct moving from upstream to downstream within the injection network 26, from the supply joint 49 indicated by point "L0" to the nozzle 20 indicated by point "L1", as shown in Figure 5.

[0080] Therefore, when the low temperature point 75 reaches the processing temperature "Ti", the blowing network 26 is not heated uniformly, but rather according to a gradient that decreases with length "L" as it moves from upstream to downstream from the supply joint 49. Thus, the second step "E2" of injecting the sterilization gas mixture is initiated before the blowing network 26 is heated to a uniform temperature. This allows the second step "E2" of injecting the sterilization gas mixture to be triggered more quickly, and thus the total time and energy consumed by the method can be reduced.

[0081] The processing temperature "Ti" is higher than the condensation temperature "Td" of the water vapor and vaporized sterilizer at the low temperature point 75 in order to avoid condensation of the vaporized oxidizing agent and / or water vapor.

[0082] To determine when the low temperature point 75 has reached the processing temperature "Ti", for example, a temperature probe 76 is placed at the low temperature point 75. This probe 76 measures the temperature trend during the first heating step "E1", and when the measured temperature condition "C1" is equal to the processing temperature "Ti", the second step "E2" of injecting the sterilization gas mixture is initiated.

[0083] In modifications of the present invention not shown, the time required to reach the processing temperature "Ti" at the coldest point is determined experimentally. Then, a second step "E2" of injecting the sterilization gas mixture is started at the end of this time.

[0084] Clearly, along step "E2" of the injection of the sterilization gas mixture, the temperature at the low point of 75 continues to rise above the processing temperature "Ti" under the influence of the passage of the sterilization gas mixture, which exhibits substantially the same temperature "Tg" as the dry gas. Consequently, the saturated vapor pressure of the mixture of vaporized sterilizer and water vapor also increases. This ensures that no condensation occurs during this second step "E2" of the injection of the sterilization gas mixture.

[0085] The first heating step "E1" further allows for a greater reduction in the relative humidity within the duct of the blowing network 26. Condensed water can actually hinder the efficiency of the sterilization method and degrade the duct of the blowing network 26. According to a modified version of the invention not shown, the relative humidity of the gas present in the duct of the blowing network 26 is measured, for example, by a relative humidity sensor 78, to ensure that the duct of the blowing network 26 is dry enough to initiate the second step "E2" of injecting the sterilization gas mixture, particularly when the relative humidity is below a threshold of, for example, 40%. The relative humidity is measured here at the low temperature point 75 of the blowing duct. Thus, in the sterilization gas mixture at the low temperature point 75, the amount of water vapor includes not only the amount of water vapor present in the sterilization vapor but also the amount of water vapor already present in the duct.

[0086] The processing temperature "Ti" is determined such that the relative saturation "RS" at the low temperature point 75 of the injection network 26 is within a determined range of 70% to 90%, preferably between 80% and 90%.

[0087] This upper limit of the range allows for a margin of error to ensure that condensation does not occur within the duct of the blowing network 26.

[0088] Lowering this range offers two advantages. First, it allows for a more rapid initiation of the sterilization gas mixture step "E2". Second, it has been found that the sterilization operation is far more effective when the ratio "RS" is high.

[0089] The relative saturation "RS" is measured here at the low temperature point 75 of the inlet duct by a relative saturation "RS" sensor 80. This is the same device that serves as, for example, the relative saturation "RS" sensor 80, the relative humidity sensor 78, and the temperature probe 76. The device is formed by a probe sold by Vaisala under the trademark name "PEROXCAP" with reference number "HPP272". Such a device makes it possible to easily consider the presence of residual water vapor in the inlet network 26 at the end of the first heating step "E1".

[0090] Figure 6 shows the trend of the relative saturation "RS" as a function of time at the low temperature point 75 in this method.

[0091] In the first heating step "E1", the blowing network 26 does not yet contain vaporized sterilizer and only contains water vapor, so the relative saturation "RS" actually corresponds to the relative humidity "RH". The relative saturation "RS" decreases regularly under the influence of the temperature rise of the low point 75 caused by the passage of dry gas. When the processing temperature "Ti" is reached, the relative saturation "RS" falls below the determined threshold.

[0092] In the second step "E2" of injecting the sterilization gas mixture, the relative saturation "RS" increases regularly to reach a determined range. This is maintained within the determined range by maintaining the flow of the sterilization gas mixture in the blowing network 26 until the end of the second step "E2" of injecting the sterilization gas mixture.

[0093] Finally, in the third step of aeration, "E3," the relative saturation "RS" gradually decreases again under the influence of pure dry gas, which expels the sterilization gas mixture from the blowing network 26.

[0094] The relative saturation level "RS" condition "C2" is periodically tested during the second step "E2" of injecting the sterilization gas mixture. When sensor 78 detects a relative saturation level "RS" higher than 90%, sensor 78 sends a signal to an electronic control unit (not shown), as indicated by the symbol "S1," which in turn instructs the sterilization fluid dispenser 72 and / or the regulating valve 74 to close, thereby preventing sterilization vapor from reaching the infusion network 26 and thus preventing condensation.

[0095] A controlled supply source 62 of sterilization steam is controlled at a constant flow rate in the second step "E2" of the sterilization gas mixture injection of the sterilization method. Distributing devices that generate pulsed flow rates, such as peristaltic pumps, are not considered, in the sense of the present invention, to be devices capable of generating a constant steam flow rate.

[0096] According to the second embodiment of the sterilization method shown in Figure 7, the controlled supply source 62 of sterilization steam has a flow rate that can occupy at least one intermediate flow rate between zero flow rate and maximum flow rate throughout the entire sterilization method.

[0097] The flow rate can be changed continuously, for example. In this case, the distribution device 72 is formed by a flow-rate adjustable valve.

[0098] In variations not shown, the flow rate can be discretely varied. The distribution device 72 is formed, for example, by multiple ducts of different flow paths arranged in parallel between the sterilization liquid tank 64 and the evaporator 66. A common multi-directional distribution valve allows the liquid to be directed to one or the other of the ducts to vary the flow rate.

[0099] In this embodiment, the saturated vapor flow rate in the mixing chamber 70 is controlled as a function of measurements made by the sensor 78 to maintain the saturated vapor partial pressure at the low temperature point 75 as close as possible to the upper limit of the determined range. For example, if the relative saturation level "RS" falls below the lower limit, e.g., 80%, the sterilization vapor flow rate is increased in adjustment operation "E4".

[0100] The sterilization method carried out according to the teachings of the present invention is rapid and protects the ducts of the blowing network 26 from corrosion. These objectives are achieved simultaneously by initiating the second step "E2" of injecting the sterilization gas mixture before the entire blowing network 26 is uniformly heated, while ensuring a temperature sufficient to avoid condensation of vaporized oxidizer.

[0101] This method is also highly efficient. This efficiency is ensured by maintaining a fairly high relative saturation level "RS" throughout the second step "E2" of injecting the sterilization gas mixture.

Claims

1. A method for sterilizing a molding machine (10) for molding containers from preforms made of thermoplastic material, the molding machine (10) comprising a blowing network (26) with ducts connecting a controlled source (24) of compressed blowing gas to at least one blowing nozzle (20) for molding the containers by blowing, the molding machine (10) comprising a device (46) for sterilizing the blowing network (26), the device comprising: a controlled source (48) of pressurized hot dry gas, distinct from the controlled source (24) of blowing gas, connected to the blowing network at a supply junction (49); a controlled source of sterilizing steam (62) containing a vaporized oxidizer; a chamber (70) for mixing the sterilizing steam with the dry gas to form a sterilizing gas mixture including vaporized oxidizer and water vapor; Equipped with The method comprises: - a step (E1) of heating the ducts of the blowing network (26) only by injection of pressurized hot dry gas, during which the dry gas heats the inner walls of the ducts of the blowing network (26); a second step (E2) of injecting a sterilizing gas mixture into the insufflation network (26); Equipped with 1. A method comprising a step of measuring a treatment temperature (Ti) by means of a probe (76) placed at the coldest point of the blowing network (26) exposed to the sterilization gas mixture, called the cold point (75), characterized in that a second step (E2) of injecting a sterilization gas mixture is started when the cold point (75) reaches a treatment temperature (Ti) higher than the condensation temperature (Td) of the water vapor and the vaporized sterilant at said cold point (75), the treatment temperature (Ti) being lower than the temperature (Tg) of the hot dry gas obtained at the supply junction (49).

2. 2. The method according to claim 1, characterized in that the treatment temperature (Ti) is determined so that the ratio, called the relative saturation (RS), between the partial pressure of the mixture of water vapor and vaporized sterilant and the saturated vapor pressure of said mixture at the cold point (75) of the blowing network (26) is in a determined range spanning from 70% to 90%.

3. The method of claim 2, wherein the determined range ranges between 80% and 90%.

4. Method according to any one of the preceding claims, characterized in that the relative saturation (RS) is measured at a cold point (75) of the injection network (26) by means of a sensor (80).

5. The method according to any one of the preceding claims, characterized in that the temperature (Tg), humidity and pressure of the drying gas at the supply junction (49) are constant.

6. The method according to any one of the preceding claims, characterized in that the controlled source (48) of drying gas is controlled at a constant flow rate throughout the entire duration of the sterilization method.

7. 7. The method according to any one of claims 1 to 6, characterized in that the controlled source (62) of sterilizing steam is controlled at a constant flow rate during the second step (E2) of injecting the sterilizing gas mixture of the sterilization method.

8. 7. The method according to claim 1, wherein the controlled source of sterilizing steam (62) has a flow rate that can occupy at least one intermediate flow rate between zero flow rate and a maximum flow rate throughout the sterilization method.

9. 9. The method according to claim 8, characterized in that the flow rate of the sterilizing steam in the mixing chamber (70) is controlled according to measurements performed by a sensor (80) so as to keep the relative saturation (RS) at the cold point (75) within a determined range.

10. A molding machine (10) for carrying out the method according to any one of claims 1 to 9, comprising a blowing network (26) with ducts connecting a controlled source (24) of compressed blowing gas to at least one blowing nozzle (20) for forming containers by blowing, the molding machine (10) comprising a device (46) for sterilizing the blowing network (26), the device comprising: a controlled source (48) of pressurized hot dry gas, distinct from the controlled source (24) of blowing gas, connected to the blowing network at a supply junction (49); a controlled source of sterilizing steam (62) containing a vaporized oxidizer; a chamber (70) for mixing the sterilizing steam with the dry gas to form a sterilizing gas mixture including vaporized oxidizer and water vapor; Equipped with A molding machine (10), characterized in that it comprises a temperature probe (76) arranged at the coldest point, called the cold point (75), of the blowing network (26) exposed to the sterilizing gas mixture, for measuring the temperature in the nozzle (20) or in a duct of the blowing network (26) adjacent to the nozzle (20).

Images