Device for providing a liquid polymer component with a predetermined air content, in particular for the production of a plastic foam

Description

[0001] The invention relates to a device for providing a liquid polymer component with a predetermined air content, in particular for the production of a plastic foam, according to the preamble of claim 1.

[0002] In the production of permanently elastic plastic foams, which are prepared by mixing two individual components such as polyol and isocyanate in a mixing device and are applied directly to the components to be sealed, such as covers or frame parts, before reacting to create a seal, it is necessary to load one of the two liquid polymer components - usually polyol - with a well-defined amount of air in order to obtain a desired foam consistency in the final product.

[0003] The problem here is that the liquid polymer components are usually provided in large containers during the mixing process, which leads to the air concentration in the liquid polymer component dropping as it is refilled into the storage container. Since it usually takes a certain amount of time, e.g. 30 minutes, for the introduced air to mix with the liquid until complete saturation, the foam quality changes constantly during this time. Accordingly, it is desirable to determine the current air content in the liquid polymer component in order to be able to increase or decrease it accordingly as needed in order to adjust the desired air content to a value that is as constant as possible within the shortest possible time.

[0004] In this context, it is known from EP 098 04 280 A1 and EP 0 451 752 A2 to use measuring cylinders with volumetric flasks to determine the air content in the liquid polymer component of a foam system, into which a defined quantity of the air-laden polymer component taken from the storage container is introduced at predetermined time intervals.

[0005] In the enclosed space of the measuring cylinder, the gas content in the sample taken from the storage container is determined by compression and / or decompression. The method and the associated device described in EP 98 04 280 have the disadvantage that the air content of the liquid polymer component cannot be determined continuously, but only in batches. Furthermore, the compression and decompression of the sample taken takes a comparatively long time, which further increases the inaccuracy between the determined air content in the sample and the actual air content of the liquid polymer component in the storage container due to the time lag and the non-linear saturation behavior of the air in the liquid polymer component.

[0006] Further devices for measuring the gas loading of liquid plastic components are known from EP 0 516 904 A1, DE 32 44 037 A1 and DE 297 12 263 U1, in which the gas loading is also determined using measuring cylinders.

[0007] Finally, DE 20 2018 104 456 U1 describes an autoclave with a reaction chamber for triggering and / or promoting chemical or physical pressure reactions, in which the oxygen content in the reaction chamber is detected by an oxygen sensor in order to flush the reaction chamber based on the detected oxygen content.

[0008] Accordingly, it is an object of the present invention to provide a device for providing a liquid, aerated polymer component, the air content of which can be continuously detected and adjusted to a desired preset value in a short time.

[0009] This object is achieved according to the invention by a device having the features of claim 1.

[0010] Further features of the invention are described in the subclaims.

[0011] According to the invention, a device for providing a liquid polymer component with a predetermined air content, such as is used in particular for the production of a plastic foam, comprises a pressure vessel into which the liquid polymer component is fed through an opening. The feed takes place discontinuously depending on the fill level or at predetermined time intervals, e.g., every 30 minutes or once a day.

[0012] The device further comprises a pipeline arranged at the bottom of the pressure vessel, which is preferably designed as a tubular screw, which has a plurality of air outlet nozzles to which air is supplied from a compressed air source arranged outside the pressure vessel 4 with a predetermined overpressure, which air exits from the air outlet nozzles into the interior of the pressure vessel and is physically dissolved in the liquid polymer component.

[0013] The device further comprises a motor-driven stirring device, in particular a variable-speed one, which mixes the liquid polymer component with the air exiting from the air outlet nozzles, so that the air physically dissolves in the liquid polymer component. As a result, the proportion of air in the liquid polymer component increases increasingly after the addition of the unladen liquid polymer component, whereby the maximum achievable saturation, or its increase per unit of time, varies and depends on the air pressure in the pressure vessel, the chemical properties of the polymer component, and also the temperature. The air dissolved in the liquid first polymer component formsAfter mixing the polymer component with the other liquid polymer component, cores for air bubbles are formed, which form the closed cavities in the cured 2-component plastic foam, which influence the permanently elastic properties as well as the pore size and compressibility of the plastic foam.

[0014] The device according to the invention is characterized in that an oxygen sensor is arranged in the circulation line, which sensor detects an actual value for the oxygen saturation of the air-laden polymer component. The device further comprises an electronic control and regulation device which is designed to change the pressure and / or the quantity of compressed air supplied to the air outlet nozzles as a function of the actual value for the oxygen saturation in the circulation line detected by the oxygen sensor, in such a way that the oxygen saturation of the liquid polymer component circulating in the circulation line assumes a predetermined target value or approaches such a predetermined target value. If desired, the oxygen partial pressure in the liquid polymer component can be determined mathematically from the oxygen saturation, if this is required for further applications.

[0015] The oxygen sensor used is preferably a sensor that operates according to the luminescence method. Such sensors are known, for example, from EP 2 461 154. The oxygen sensor 100 is preferably mounted in the circulation line using an adapter and can thus continuously measure the amount of bound oxygen in the polymer during operation, so to speak "inline." The oxygen sensor has a photosensitive membrane as a contact surface with the polymer. A luminophore located in the sensor or membrane is excited and subsequently emits light (fluorescence). If oxygen then flows past the sensor, the emission of the luminophore is reduced proportionally to the amount of oxygen in front of the sensor, which is also referred to as the quenching effect.Preferably, depending on the change in luminophore emission, software in the electronic control and regulation device then calculates the oxygen content in the liquid polymer component in the region behind the photosensitive membrane. The oxygen content is preferably converted into a value for the amount of air bound in the polymer. Using this value for the amount of air bound in the polymer, the further air loading of the liquid polymer components in the pressure vessel, which simultaneously serves as the storage container for the liquid polymer component, is then regulated by changing the supply duration and / or the pressure of the air supplied from outside into the pipe arranged in the pressure vessel.

[0016] As recognized by the applicant, the basic idea of ​​the invention, in simple terms, is to measure the physically bound oxygen content in the liquid polymer continuously or at predetermined time intervals and to use this to determine the content of bound air in the polymer. Using the amount of bound air in the polymer detected by the oxygen sensor, the air loading of the polymer is subsequently regulated by increasing the pressure in the pressure vessel and / or changing the amount of air fed into the vessel per unit time in order to thereby maintain a preferably constant ratio of polymer to air, which in turn is crucial for a consistent quality of the polymer foam mixture after mixing the two polymer components.

[0017] The invention is described below with reference to a preferred embodiment of the invention and the accompanying drawings. In the drawings: Fig. 1 is a schematic overview of the device according to the invention, and Fig. 2 is a schematic partial representation of the circulation line with the oxygen sensor arranged thereon.

[0018] As in Fig. 1 As shown, a device 1 for providing a liquid first polymer component 2A with a predetermined air content comprises a pressure vessel 4, to which the liquid polymer component 2A is supplied, for example, via an opening 6 closed by the lid 4c of the pressure vessel 4 or an opening (not shown) in the vessel wall 4a.

[0019] As in Fig. 1As shown, a pipeline 8 is arranged in the region of the bottom 4b of the pressure vessel 4. This pipeline has a plurality of air outlet nozzles 10, to which air is supplied at a predetermined overpressure from a compressed air source 12 arranged outside the pressure vessel 4, e.g., an air compressor. This air flows out of the air outlet nozzles 10 and is physically dissolved in the first polymer component 2A stored in the interior of the pressure vessel 4.

[0020] The device 1 further comprises a stirring device 14 driven by a motor 13, which in Fig. 1is indicated by a schematic rotor, and which mixes the liquid polymer component 2A with the compressed air emerging from the air outlet nozzles 10, so that the latter physically dissolves in the liquid polymer component 2A and its air content, which forms nuclei for air bubbles when the polymer component is mixed with another liquid polymer component 2B, increases accordingly.

[0021] As the representation of the Fig. 1can continue to be removed, the interior of the pressure vessel 4 is fluidly connected to a circulation line 20 via an inlet 22 arranged in the region of the bottom 4b of the pressure vessel 4, through which circulation line the liquid polymer component 2A is circulated by means of a pump 26 back to an outlet 24 which is located above the inlet 22. As shown, the outlet 24 preferably comprises a vertical pipe section extending downwards from the passage opening (not designated in more detail) in the vessel wall 4a, which is preferably located below the liquid surface of the liquid polymer component 2A. This ensures that the liquid 2A circulated back into the pressure vessel 4 via the outlet 24 flows against the amount of air rising from the air outlet nozzles 10 (countercurrent principle), whereby the loading of the liquid polymer component 2A with air is advantageously improved.

[0022] Between the pump 26 and the outlet 24, a known outlet valve 30 is arranged, via which the air-laden liquid polymer component 2A can be fed to a known mixing device 40 in order to mix the first liquid polymer component 2A with the further liquid polymer component 2B in a known manner in a mixing device 40 symbolically indicated by a Y-line. Preferably, the mixed polymer components 2A, 2B, which emerge from the mixing device 40 as liquid, uncured plastic foam 2A + 2B, are applied directly and continuously as a bead onto a component, such as a lid or a door, on which the plastic foam mixture, after curing, forms, for example, a corresponding permanently elastic seal.The first liquid polymer component 2A, which is loaded with a predetermined amount of air for core formation in the device 1 according to the invention, can be, for example, polyol, and the second polymer component 2B is in this case isocyanate.

[0023] An oxygen sensor 100 is arranged in the circulation line 20, which preferably continuously records an actual value for the oxygen saturation of the air-laden polymer component 2A. The device 1 further comprises an electronic control and regulation device 50, which is connected via lines not designated in more detail to the oxygen sensor 100, as well as to the pump 26, which is preferably a metering pump, and to an on / off valve 42, via which the pressure and / or the quantity of compressed air supplied to the air outlet nozzles 10 from the compressed air source 12 can be changed depending on the actual value for the oxygen saturation in the circulation line 20 recorded by the oxygen sensor 100. For this purpose, the pressure and / or the quantity of compressed air supplied to the air outlet nozzles is increased or decreased in such a way that:reduce that the oxygen saturation in the liquid polymer component 2A circulating in the circulation line 20 assumes a predetermined target value or approaches such a predetermined target value.

[0024] In one embodiment of the invention, the aforementioned on / off valve 42 is opened and closed again by the electronic control and regulation device 50 for a predetermined period of time, e.g., for 5 minutes, the length of which is increased, e.g., by 10% or a fixed time value, e.g., 10 seconds, if the actual oxygen saturation value detected by the oxygen sensor 100 is lower than the preferably empirically determined target value. By opening the on / off valve 42, compressed air flows, preferably via a flow meter 16, from the compressed air source 12 into the pipeline 8 and enters the liquid polymer component 2A through the air outlet nozzles 10, in which a portion of the air is physically dissolved in the liquid polymer component depending on the pressure within the pressure vessel 4, the current degree of saturation, and the temperature.The part of the supplied air that is not released rises and exits via an air outlet channel 60 on the top of the pressure vessel 4, which can be closed by a pressure regulating valve.

[0025] In a correspondingly reversed manner, the time during which compressed air flows from the compressed air source 12 through the on / off valve into the pressure vessel 4, and thus the amount of supplied air, is shortened by the electronic control and regulation device 50 if the instantaneous actual value detected by the oxygen sensor 100 exceeds the setpoint. If the actual value is equal to or substantially equal to the setpoint for the oxygen saturation, the valve 42 is preferably closed until the unloaded first liquid polymer component 2A is supplied again.

[0026] As in Fig. 1As indicated, the pressure vessel 4 has an air outlet channel 60 arranged in the vessel wall 4a or in the vessel lid 4c, which communicates in terms of flow with the air volume located in the pressure vessel 4 above the liquid polymer component 2A, and which is in flow connection with the environment via a pressure regulating valve 62, which opens when the pressure inside the pressure vessel 4 exceeds a predetermined maximum pressure.

[0027] The pressure regulating valve 62 is preferably a pneumatically controllable 3 / 2-way valve, whose control input 62I can be supplied with a predetermined, variable control pressure, preferably from a further compressed air source 64. The flow connection between the interior of the pressure vessel 4 and the environment is released by the pressure regulating valve 62 when the pressure in the interior of the pressure vessel 4 exceeds the control pressure, which can be sensitively and preferably mechanically adjusted to 4 bar, for example, via a needle valve (not shown in detail). As shown in Fig. 1 As is indicated purely schematically, the valve body 63 in the pressure regulating valve 62 is forced into the unspecified valve seat by the applied control pressure of the further compressed air source 64 in order to prevent the compressed air from escaping from the interior of the pressure vessel 4 into the downstream air outlet channel 60 and via this into the environment.

[0028] This embodiment of the invention has the advantage that the pressure in the interior of the pressure vessel 4 can advantageously be very sensitively adjusted to a predetermined value without the need for a complex electronic pressure control device, which can, however, also be used alternatively. At the same time, it is ensured that the compressed air introduced into the pressure vessel 4 from the compressed air source 12 during the previously mentioned time intervals, which can, for example, have a pressure of 4.5 bar or more, can escape from the interior of the pressure vessel 4 when the control pressure of the further compressed air source 64 is exceeded. This is the basic prerequisite for a substantially constant air flow in the liquid polymer component 2A, which considerably facilitates control to a predetermined target value for the oxygen saturation of the liquid polymer component 2A and advantageously increases the control accuracy.

[0029] A further advantage of the previously described embodiment of the invention is that the pressure regulating valve 62 is automatically closed, so to speak, when the pressure in the pressure vessel 4 falls below the control pressure as a result of the air continuously flowing out of the air outlet channel 60 after the on / off valve 42 of the compressed air source 12 has been closed, without any additional electronically controlled valves or other components being required for this purpose.

[0030] According to a further idea underlying the invention, at least one Fig. 1The pressure sensor 28 shown is arranged, which measures the pressure of the air-laden liquid polymer component in the circulation line 20 for calibrating the oxygen sensor 100. This allows the oxygen sensor 100 to be calibrated with high accuracy, thereby further increasing the overall measurement accuracy with which the oxygen saturation of the liquid polymer component 2A can be determined.

[0031] In the preferred embodiment of the invention, the pressure sensor 28 and the oxygen sensor 100 are arranged upstream of the pump 26, i.e., between the outlet 24 of the pressure vessel 4 and the pump 26 in the circulation line 20. This provides the advantage that pressure fluctuations in the circulation line 20 caused by the removal of the liquid polymer component 2A in the mixing device 40 have no influence, or only a significantly reduced influence, on the pressure of the liquid polymer component 2A when determining the oxygen saturation in the oxygen sensor 100.This allows the actual value for the oxygen saturation of the liquid polymer component 2A to be recorded with high accuracy by the oxygen sensor even while the liquid polymer component 2A is being fed to the mixing device 40, whereby quality fluctuations in the finished foam mixture, which result from an excessively high or too low oxygen content in the liquid polymer component 2A, can be counteracted at an early stage. Particularly preferably, the pressure sensor 28 is arranged at the level of the oxygen sensor 100 on the opposite side of the circulation line 20. At the same time or alternatively, it can be arranged downstream of the pump / metering pump 26, as shown in FIG. Fig. 1is also indicated schematically. Furthermore, it may be provided that a shut-off valve, preferably a mechanically operated ball valve, is arranged in the circulation line 20 upstream of the oxygen sensor 100, with which the flow of the liquid polymer component 2A can be manually interrupted in the event of a malfunction or to shut down the device 1.

[0032] In the preferred embodiment of the invention, the oxygen sensor 100 has a photosensitive membrane 102 with a luminophore contained therein, which forms an inner wall portion 20a of the circulation line 20, as shown in Fig. 2is shown. The air-laden liquid polymer component 2A comes into direct contact with the luminophore as it flows through the circulation line 20. The oxygen sensor 100 further comprises a light source 104, e.g., an LED, which irradiates the photosensitive membrane 102 with electromagnetic radiation, preferably short-wave blue light. The oxygen sensor 100 further contains an optical sensor 106 which detects the light emitted by the irradiated membrane 102 and is connected to associated sensor electronics 108, which generates an electrical signal from the light detected by the optical sensor 106, the magnitude of which is a measure of the saturation of the liquid polymer component 2A with the oxygen contained therein. Such oxygen sensors are known in the art, for example, from the aforementioned EP 2 461 154 A1, and can be purchased commercially as ready-made units.

[0033] In order to determine the actual value for the amount of air contained in the liquid polymer component 2A as an absolute value, the electronic control and regulation device 50 is advantageously configured to determine the amount of air contained in the liquid polymer component 2A per unit volume or per unit mass of the liquid polymer component 2A as an absolute value from the actual value for the oxygen saturation determined by the oxygen sensor 100 and the sensor electronics 108 coupled thereto. This is then fed as a control parameter in a known manner to an electronic controller, e.g., a PID controller, which is preferably implemented in software in the electronic control and regulation device 50.For this purpose, the electronic control and regulation device 50 is configured to determine the amount of air contained in the liquid polymer component 2A per unit volume and / or per unit mass on the basis of values ​​previously determined empirically by measurements for the oxygen saturation and the associated amount of air contained in the liquid polymer component 2A, which can be stored in a memory 52 of the electronic control and regulation device 50. The values ​​for the oxygen saturation and the amount of air per unit volume / unit mass are preferably previously determined on the basis of compression and decompression measurements, as described, for example, in EP 098 04 280 A1 or EP 0 451 752 A2, and are permanently stored as value pairs in the memory 52. List of reference symbols

[0034] 1Device according to the invention 2ALiquid polymer component 2BFurther polymer component 4Pressure vessel 4aVessel wall 4bBottom 4cTank lid 6Tank opening 8Pipe 10Air outlet nozzles 12Compressed air source 13Motor 14Agitator 16Flow meter 20Circulation line 20aInner wall section 22Inlet 24Outlet 26Pump 28Pressure sensor 30Outlet valve 40Mixing device 42On / off valve 50Electronic control and regulation device 52Memory of the electronic control and regulation device 60Air outlet channel 62Pressure regulating valve 62Control input of the pressure regulating valve 63Valve body 64Additional compressed air source 66Air outlet 100Oxygen sensor 102Photosensitive membrane 104Light source 106Optical sensor 108Sensor electronics

Claims

1. An apparatus (1) for providing a liquid polymer component (2A) having a predefined air content, in particular for producing a plastic foam, comprising a pressure vessel (4), to which the liquid polymer component (2A) can be fed through an opening (6), a pipeline (8), in particular tubular screw conveyor, which is arranged on the bottom (4b) of the pressure vessel (4) and has a multiplicity of air outlet nozzles (10), to which air from a compressed-air source (12) arranged outside the pressure vessel (4) can be fed at a predefined pressure in order to exit the air outlet nozzles (10) into the interior space of the pressure vessel (4), a motor-operated stirring device (14), which mixes the liquid polymer component (2A) with the air exiting the air outlet nozzles (10), a circulation line (20) having an inflow (22) arranged in the region of the bottom (4b) of the pressure vessel (4) and an outflow (24) arranged above the inflow (22), a pump (26), which is arranged between the inflow (22) and the outflow (24) and conveys the air-charged polymer component (2) through the circulation line (22) from the inflow (22) to the outflow (24), and an outlet valve (30), which is arranged between the pump (26) and the outflow (24) and which makes it possible to feed the air-charged liquid polymer component (2A) to a mixing device (40) for mixing with a further polymer component (2B), characterized in that an oxygen sensor (100) is arranged in the circulation line (20) and measures an actual value for the oxygen saturation of the air-charged polymer component (2A), and in that an electronic control device (50) is provided, which is configured to modify the pressure and / or the amount of compressed air fed to the air outlet nozzles (10) on the basis of the actual value for the oxygen saturation measured by the oxygen sensor (100), in such a way that the oxygen saturation of the liquid polymer component (2A) circulating in the circulation line (20) assumes a predefined setpoint value.

2. The apparatus as claimed in claim 1, characterized in that the compressed-air source (12) can be fluidically connected to the pipeline (8) via an open-close valve (42), which can be actuated by the electronic control device (50), and in that the electronic control device (50) opens the open-close valve (42) for a predefined period of time if the actual value measured by the oxygen sensor (100) is less than the setpoint value for the oxygen saturation.

3. The apparatus as claimed in either of the preceding claims, characterized in that a pressure sensor (28) is arranged in the circulation line (20) and measures the pressure of the air-charged liquid polymer component in the circulation line (20) to calibrate the oxygen sensor (100).

4. The apparatus as claimed in claim 3, characterized in that the pressure sensor (28) and the oxygen sensor (100) are arranged upstream of the pressure vessel (4) in the line (20).

5. The apparatus as claimed in one of the preceding claims, characterized in that the pressure vessel (4) has an air outlet channel (60), which is arranged in the vessel wall (4a) or in the vessel cover (4c), fluidically communicates with an air volume provided in the pressure vessel (4) above the air-charged liquid polymer component (2A), and is fluidically connected to the surrounding area via a pressure regulating valve (62) which opens if the pressure inside the pressure vessel (4) exceeds a predefined maximum pressure.

6. The apparatus as claimed in claim 5, characterized in that the pressure regulating valve (62) is a pneumatically controllable 3 / 2-way valve, to the control input (62I) of which a predefined variable control pressure from a compressed-air source (12) can be applied, wherein the fluidic connection between the interior space of the pressure vessel (4) and the surroundings is opened up by the pressure regulating valve (62) if the pressure in the interior space of the pressure vessel (4) exceeds the control pressure.

7. The apparatus as claimed in one of the preceding claims, characterized in that the oxygen sensor (100) comprises a photosensitive membrane (102) containing a luminous phosphor, which forms an inner wall portion (20a) of the circulation line (20) and comes into contact with the air-charged liquid polymer component (2A) when the latter flows through the circulation line (20), and in that the oxygen sensor (100) also comprises a light source (104) which can irradiate the photosensitive membrane (102) with electromagnetic radiation, and also an optical sensor (106) that detects light emitted by the irradiated membrane (102) and sensor electronics (108), which are coupled to the optical sensor and generate an electrical signal, the value of which is a measure for the oxygen saturation of the liquid polymer component (2A), from the light detected by the optical sensor (106).

8. The apparatus as claimed in claim 7, characterized in that the electronic control device (50) is configured to determine the amount of air present in the liquid polymer component (2A) per unit volume or per unit mass of the liquid polymer component (2A) from the value ascertained for the oxygen saturation.

9. The apparatus as claimed in claim 8, characterized in that the electronic control device (50) is configured to determine the amount of air present in the liquid polymer component (2A) per unit volume and / or per unit mass on the basis of values for the oxygen saturation and the associated amount of air present in the liquid polymer component (2A) that were ascertained empirically by measurements beforehand, and which are storable in a memory (52) of the electronic control device (50).