Press for manufacturing sandwich products

Abstract

A press (10) for manufacturing sandwich panels comprises a first pressure plate (12) and a second pressure plate (14) which are movable relative to each other. The pressing tool (12; 14) is provided with at least one internal flow channel (16). The press (10) has a fluid circulation circuit for heating and cooling. The press includes a heater (34) for generating hot pressurized water in communication with the pressing tool (12, 14) and includes an outlet pressure control valve (58) configured to convert the hot pressurized water into steam in communication with the pressing tool (12, 14) during initial rapid cooling.

Description

[0001] The present invention relates to a press for in situ manufacturing of sandwich products, in particular thermoplastic sandwich panels, comprising a foamed thermoplastic core between cover layers, and to a manufacturing method using such a press.

[0002] It is known in the art to manufacture sandwich panels on site from a starting structure. For example, EP636463 discloses such a method. The on-site manufacture according to EP636463 comprises at least the step of providing a starting structure, the starting structure comprising a core layer of thermoplastic material, wherein a physical foaming agent (in particular a swelling agent) is incorporated and covered with a skin layer at at least one surface. Typically, the core layer is arranged between two skin layers, advantageously between fiber-reinforced thermoplastic skin layers. The starting structure is positioned in a heated press between a bottom platen and a top platen. Subsequently, the press is closed and the plates apply pressure on the starting structure. The starting structure is heated to the foaming temperature of the thermoplastic material (higher than the boiling temperature of the swelling agent) while continuing to apply pressure on the starting structure to prevent premature foaming. During heating, the swelling agent migrates from the core layer of the starting structure into the skin layer, thereby producing adhesion between the core layer and the skin layer. In this way, a uniform foamed layer is produced between the skin layers. Once the foaming temperature is reached, foaming is performed by moving the press plates apart to a predetermined distance in a controlled manner, thereby allowing the thermoplastic material of the core layer to expand and form foam cells by the physical foaming agent. Thus, foaming and bonding occur in the same press. Pressure is maintained on the now foamed structure and the press plates are cooled. When sufficiently cooled so that no further foaming occurs, typically below the boiling temperature of the swelling agent (e.g., at ambient temperature), the pressure can be completely released and the sandwich panel thus obtained can be removed from the press. When manufacturing thermoplastic sandwich panels with physical foaming agents, rapid cooling is required to prevent foam collapse, especially at the junction of the foam and skin layers, and if a fiber-reinforced thermoplastic skin is present, to prevent the physical foaming agent from further migrating into the thermoplastic material of the fiber-reinforced thermoplastic skin.

[0003] In the case of chemical foaming agents as described in WO 2015 / 065176 A1, the starting structure is placed in a heated press which has been heated to a temperature well above the melting temperature or melting temperature range of the thermoplastic material in the core. After the chemical foaming agent in the core layer has been decomposed, the intermediate structure obtained is cooled in an intermediate cooling step to a temperature which is generally just above the melting temperature of the corresponding thermoplastic material of the core layer. Subsequently, foaming is performed by moving the press plates away in a controlled manner while maintaining pressure on the foamed structure, and when the desired predetermined foaming thickness is reached, the press plates are further cooled.

[0004] For reasons of productivity, the multiple process steps of heating, foaming and cooling should all be rapid, e.g. in the range of tens of seconds to a maximum of several minutes, and uniform, especially during cooling, to prevent significant temperature differences on the press plates, which could affect the quality of the final sandwich panel. Rapid cooling is also necessary to prevent post-foaming and especially the collapse of the cells formed, which would severely affect the mechanical properties of the sandwich panel obtained therefrom.

[0005] WO2020 / 117048A1 discloses a press for manufacturing such a sandwich panel. This known press has a fluid circulation loop for heating and cooling the press plate. The fluid circulation loop includes a heater for generating a hot fluid, the heater having an outlet and an inlet, the outlet being connected to a fluid supply pipe, and the inlet being connected to a fluid return pipe. The fluid supply pipe is in fluid communication with the inlet fluid of at least one internal flow channel in each press plate, and the fluid return pipe is in fluid communication with the outlet fluid of at least one internal flow channel in each press plate. In addition, the fluid circulation loop is provided with a controlled expansion valve, which is configured to convert hot pressurized water into steam for cooling the press plate. The water source has an outlet that is in fluid communication with the inlet fluid of the internal flow channel of each press plate via a water supply pipe. In addition, it is disclosed that if the amount of hot pressurized water in the flow channel becomes too small and insufficient for the cooling required for the phase change, additional hot pressurized water can preferably be introduced into the flow channel. This rapid cooling method, which uses evaporation heat to convert the hot pressurized water in the press plate flow channels into steam after shutting off the flow of pressurized hot water through these flow channels, aims to improve the temperature uniformity on the surface of the press plate, especially in the initial stage of cooling.

[0006] It now appears that the large amount of steam discharged from the platen channels and supply pipes (including connectors and joints or manifolds) leads to high flow rates, so that the hot water in the flow channels is forcibly entrained and blown out together with the steam. The result is that the flow channels are emptied quickly, while they are still not fully wetted, so that the desired rapid cooling cannot be achieved during the entire cooling period, and / or the temperature above and / or between the platens is uneven, which is unacceptable. If the cooling rate is too low, especially in the initial cooling stage, the quality of the final sandwich panel will be affected. The method of adding make-up water to compensate for water loss as disclosed in WO2020 / 117048A1 does not provide a satisfactory solution.

[0007] The object of the present invention is to avoid the above mentioned disadvantages. In particular, the object of the present invention is to maintain sufficiently rapid and uniform cooling during the initial cooling of the foamed sandwich product.

[0008] A press for manufacturing a sandwich product comprising a foamed thermoplastic core between cover layers, in particular a thermoplastic sandwich product, more particularly an in situ manufactured thermoplastic sandwich panel, is defined in the appended claim 1 .

[0009] Specific embodiments of the press according to the invention are defined in the dependent claims. A method of producing a sandwich product, preferably using said press, is also defined in the claims.

[0010] The press according to the invention comprises press plates (sometimes also referred to as pressing tools) which are movable relative to each other, typically a bottom press plate and a top press plate, which are arranged above each other and can perform a movement in the vertical direction. Typically, one or both of the press plates have a cavity in which a starting structure for a sandwich product can be positioned. Typically, the periphery of the cavity engages with the periphery of the starting structure so that during the controlled foaming phase, only expansion in the thickness (vertical) direction occurs. Typical products that can be produced using such a press according to the invention include two-dimensional products (length and width are large compared to thickness), such as sandwich panels. The panels are preferably in a flat configuration, but may also have a slightly curved or corrugated shape.

[0011] The press according to the present invention comprises a heater for producing hot water, which is used for the heating and cooling phases of the manufacturing process, which will be described in detail below. The heater has a supply inlet for supplying new water, as well as a hot water outlet and a return inlet. The hot water outlet and the return inlet are connected to a fluid circulation loop. During the heating and foaming phases of manufacturing the sandwich product, a hot fluid (usually hot water) can be used to heat the press plate, wherein the heated fluid circulates through the press plate in the fluid circulation loop. Alternatively, steam can also be used to heat the press plate, but in this case, before cooling, the fluid circulation loop should be filled with hot pressurized water. An electric heater, a boiler or other heat exchanger is usually used as a heater to heat the water to the required temperature (range). The heater can be a boiler that produces hot water at a constant high delivery pressure, thereby avoiding the risk of steam bubbles forming in the supply lines and manifolds leading to the press plate. The press has a fluid circulation loop for heating and cooling the press plate during the corresponding operating phases of the press. Each press plate has at least one internal flow channel through which a fluid can flow from the flow channel inlet to the flow channel outlet, and each press plate usually has a plurality of channels. Typically, the inlet ends of the plurality of flow channels are connected to one or more supply manifolds or connectors for connecting the fluid supply pipe, and the outlet ends are connected to one or more collector manifolds or connectors for connecting the fluid return pipe. During heating, foaming and cooling, adjacent internal flow channels in the same press plate are preferably supplied in a counter-current manner. The hot water outlet of the heater is connected to the inlet end of at least one flow channel in each press plate through a fluid supply pipe. The return inlet is connected to the outlet end of at least one flow channel through a fluid return pipe. Water circulation is provided by means of one or more suitable pumps in the fluid return pipe. In order to heat the press plate, the heater prepares hot water, which is circulated to the flow channels in the press plate through the fluid supply pipe and returned from the press plate through the fluid return pipe. Considering the type of foaming agent, the temperature and pressure of the hot water supplied to the press plate are generally in the range of 170°C-250°C and 8 bar-30 bar, respectively. For physical foaming agents, lower temperatures (such as 170°C-190°C) are suitable. For chemical foaming agents that need to be decomposed, higher temperatures (such as 210°C-230°C) are generally applied. Advantageously, the distribution of the flow channels in the platen body and the flow rate through each channel of the two platens during operation is such that a uniform temperature is achieved on the inner side of the platens facing the product.

[0012] The press of the invention also has a cooling mode in which part of the cooling effect is based on the heat of evaporation required to convert the hot pressurized water into steam. The heat of evaporation required for this conversion is extracted (uniformly) from the press plate. Thus, the press plate cools the foamed structure.

[0013] The fluid return conduit of the fluid circulation loop is in controlled fluid communication with the outlet control pressure valve. In the cooling mode, the connection between the heater and the fluid circulation loop is closed. The outlet control pressure valve is then opened in the first cooling stage while hot pressurized water is circulated on the press plate. The hot water comes from at least one water source for supplying temperature-controlled water, the outlet of the water source having a valve connected to the fluid return conduit at an upstream position of the circulation pump. The pump pressurizes the hot water. The temperature and pressure of the hot pressurized water are lower than the saturation pressure of the press plate at the current temperature, such as the water temperature in the range of 170°C-250°C. Steam is mainly formed in the flow channel of the press plate and expands at and downstream of the outlet control pressure valve. In the first cooling stage, cooling by flowing hot pressurized water continues until the press plate reaches a first predetermined temperature. In order to prevent emptying of the flow channel and insufficient wetting of the internal flow channel, while ensuring that the formed steam is dissolved in the water in the internal flow channel of the press plate, the outlet pressure control valve should be opened gradually and the total flow of water is kept at a relatively low level. The first predetermined temperature is typically in the range of 105°C-125°C, such as 110°C-120°C.

[0014] Optionally, if the outlet control pressure valve is opened to atmospheric pressure, a second cooling stage is performed, wherein at least one press plate is cooled from a first predetermined temperature to a second predetermined temperature by introducing water from at least one water source in the fluid circulation loop and increasing the total water flow by controlling a pump.

[0015] Therefore, once the press plate reaches the first predetermined temperature, an optional second cooling stage can be initiated, in which the press plate is further cooled to a second predetermined temperature using water from at least one water source, wherein the at least one water source typically has a lower temperature from a temperature-controlled water source. The water temperature is typically in the range of 70°C-90°C. In this way, cooling is performed by evaporation until the press plate reaches a temperature of 100°C, and convection is continued. However, since the temperature difference between the circulating water at about 100°C and the cooled press plate is reduced in the first cooling stage, the cooling rate is slowed down and the required high cooling rate cannot be achieved. Preferably, if there is a second cooling stage, the flow rate of the second cooling stage is increased, and the temperature is set so that evaporative cooling is avoided. Therefore, in the optional second cooling stage, the water temperature is reduced and the flow rate is increased by adjusting the circulating pump, for example, in order to obtain the required cooling rate and uniformity of the temperature on the press plate, the flow rate in the second cooling stage is about 8 times-10 times the flow rate in the first cooling stage. The second predetermined temperature is typically in the range of 75°C-95°C, such as 80°C-85°C. The greater the temperature difference between the inlet temperature of the water supplied to the press plate and the temperature measured at the press plate, the lower the inlet pressure must be, corresponding to a value below the saturation pressure, which increases the risk of water entrainment in the formed steam.

[0016] If the outlet control pressure valve is connected to a sub-atmospheric environment (eg, via a vacuum pump), the press is cooled more deeply, so that the optional second cooling step can be omitted.

[0017] The press according to the present invention comprises a control device configured to operate the press under heating, foaming and cooling conditions.

[0018] In a preferred embodiment, a vacuum pump is provided on the flash tank, which reduces the first predetermined temperature of the first cooling stage and the second predetermined temperature in the second cooling stage. Applying a (partial) vacuum using a vacuum pump connected to the fluid return line via the flash vessel in question results in an additional pressure drop, thereby reducing the temperature at which steam formation occurs. This will allow continued cooling by changing the phase of water to steam to reach lower temperatures, for example below 90° C., compared to the above range of the first predetermined temperature, resulting in a more uniform temperature of the press plate.

[0019] The third slow cooling stage is performed by water cooling from a predetermined temperature (or, if the second cooling stage is performed, from a second predetermined temperature) using temperature-controlled water from at least one water source, but at a reduced cooling rate. Typically, in order to achieve uniform cooling in this stage, the temperature difference between the circulating water temperature and the platen temperature is generally kept constant, such as in the range of 1°C-15°C, preferably in the range of 3°C-12°C. If necessary, an increased flow rate can be maintained in the third cooling stage.

[0020] The press according to the invention ensures that, during the rapid first cooling phase and the optional second cooling phase, water with appropriate pressure and temperature continuously flows in sufficient quantity through the internal flow channel and the steam formed dissolves in the water flow so that the press plate can be continuously cooled. Expansion takes place at or downstream of the outlet control pressure valve.

[0021] At least one water source for supplying temperature-controlled water in the first cooling stage is configured to deliver water at about 100°C to the fluid circulation loop. In one embodiment, the outlet control pressure vessel is in fluid communication with a downstream flash tank for recovering water from the formed steam. In another embodiment, the flash tank is provided with a water outlet in fluid communication with a fluid return pipeline, the water outlet being upstream of the circulation pump and serving as one of the at least one water source. The outlet pressure control valve is connected to the downstream flash tank, which is maintained at atmospheric pressure or maintained at a reduced pressure by a vacuum pump. Then, expansion is mainly performed in the flash tank. The water recovered in the flash tank is returned to the fluid return pipeline upstream of the circulation pump. Since the recovered water from the flash tank has a temperature of 100°C at atmospheric conditions, once the recovered water is re-pressurized by the circulation pump in the fluid return pipeline, its temperature will still be lower than the press plate (i.e., the saturation pressure of the circulating water to the press is lower than the saturation pressure at the current temperature of the press plate), it is possible to continuously perform flashing and cooling in the first cooling stage until a first predetermined temperature, such as within the range of 105°C-125°C. The evaporative cooling in the first cooling stage can be continued under sub-atmospheric conditions to a lower first predetermined temperature of less than 90° C. It is also possible to replenish the water lost in the first cooling stage from another water source and set the water delivered from the flash tank to a suitable temperature by mixing it with the water delivered from the flash tank in an optional second cooling stage.

[0022] A separate temperature-controlled water source may be used in place of the recycled water from the flash tank.

[0023] Thus, during the first cooling stage and (part of) the second cooling stage, pressurized water with an elevated temperature of about 100°C flows through at least one internal flow channel in each press plate to the outlet control pressure valve. The hot pressurized water absorbs heat from the press plate and is converted into steam, thereby cooling the press plate. The steam bubbles dissolve in the hot pressurized water flow because they are still under pressure due to the continuous supply of hot pressurized water. The steam dissolved in this way expands at or downstream of the outlet pressure control valve. The absorbed heat is discharged in the form of water vapor by evaporation of the hot pressurized water. The water recovered from the flash tank has a temperature of 100°C at atmospheric pressure, and the press plate can be cooled with the 100°C water in the first cooling stage and the second cooling stage until the press plate reaches a second predetermined temperature, wherein the water absorbs the heat of the press plate and is converted into steam, which is dissolved in the constant flow of 100°C water passing through the press plate. By maintaining the pressure of the hot water at an appropriate level (below the saturation temperature at the current temperature of the press plate), the entrainment of hot pressurized water in the formed water vapor can be effectively reduced, thereby avoiding emptying of the flow channel and ensuring sufficient wetting.

[0024] The actual temperature of at least one, preferably both, press plates is monitored. The temperature of the press plate is typically measured by a temperature sensor positioned a few millimeters (e.g. 3-4 mm) below the pressing surface in the center of the press plate. From the measured temperature (e.g. the average of the measured temperatures of the two press plates), the corresponding saturation pressure at said (average) measured temperature can be calculated (e.g. using a look-up table). Advantageously, the temperature and pressure of the circulating water supplied to the press plate is also monitored.

[0025] According to the invention, heat is removed from the press plates by converting hot pressurized recycled water into steam more evenly than cooling with cold water, and yet sufficiently rapidly to achieve the desired cooling rate. Such even cooling according to the invention also results in a more even temperature on the press plate surface and / or between the press plates, leading to less local variations in density and pore size in the final sandwich panel, and to a better, more even bond between the foam and the cover layer. The quality of the manufactured sandwich panel is thereby improved.

[0026] Typically, a PLC, PC or similar device is used to control the operation of the press. In one embodiment, the controller includes a processor and a memory storing computer readable instructions, which, when executed by the processor, perform the following process, including:

[0027] preheating the platen by flowing a hot fluid through a fluid heating circulation loop;

[0028] closing the press by moving the preheated press plates towards each other and applying pressure on the starting structure of the sandwich panel to be manufactured;

[0029] The starting structure is heated to a foaming temperature while pressure is applied to the starting structure:

[0030] (If the heat content of the preheated platen is insufficient to bring the starting structure to the foaming temperature, the platen is further heated by flowing a hot fluid through the fluid circulation loop);

[0031] foaming the starting structure at a foaming temperature by moving the platens apart a predetermined distance while maintaining pressure on the foaming structure; typically, a desired thickness is achieved at the end of the foaming curve;

[0032] interrupting the flow of hot fluid from the heater to the fluid circulation loop;

[0033] In the first cooling stage, the outlet pressure control valve is opened and temperature-controlled water from at least one water source (such as a flash tank) is flowed through the fluid circulation loop by means of a circulation pump, thereby cooling the press plate to a first predetermined temperature, wherein the temperature and pressure of the temperature-controlled water are lower than the saturation pressure of the press plate at the current temperature.

[0034] Optionally, in a second cooling stage, the press plate is cooled from the first predetermined temperature to a second predetermined temperature by flowing temperature-controlled water from at least one water source at an increased water flow rate,

[0035] And, in the third cooling stage, water cooling from the first predetermined temperature or the second predetermined temperature to the ambient temperature is performed at a reduced cooling rate by flowing temperature-controlled water from at least one water source (eg, a separate water source).

[0036] Typically, opening the press to allow removal of the produced sandwich panels is also included in the instructions.

[0037] In one embodiment, instructions for a cooling platen process include measuring a current temperature of at least one platen via a temperature sensor, determining a saturation pressure of hot water at the measured temperature of the at least one platen, and setting an inlet pressure of hot pressurized water supplied from a heater to the platen.

[0038] In another embodiment, the instructions for cooling the platen process include setting an inlet temperature of hot pressurized water supplied to the platen to be equal to or lower than a measured temperature of the platen.

[0039] Advantageously, the press is provided with a supply unit for introducing the starting structure into the press (instead of manually arranging the starting structure in the press) and / or a discharge unit for unloading the produced sandwich panels from the press. The instructions then additionally comprise introducing the starting structure into the press and, if applicable, removing the produced sandwich panels from the press.

[0040] The above instructions are generally used for the manufacture of sandwich panels using physical foaming agents. A physical foaming agent is a swelling agent (i.e. a solvent with low solubility in the corresponding thermoplastic material) or a solvent that volatilizes when heated and the resulting bubbles generate foam cells. Examples of physical foaming agents include carbon dioxide and light hydrocarbons (such as various pentanes) as well as swelling agents such as acetone and solvents such as dichloromethane.

[0041] For thermoplastic sandwich panels manufactured using chemical foaming agents, such as described in WO2015 / 065176A1, it is advantageous to quickly and evenly cool from the decomposition temperature (or higher) of the foaming agent to the foaming temperature, and from the foaming temperature to a temperature below the Tg or Tm of the thermoplastic material in the foam core of the thermoplastic sandwich panel, so as to reduce internal stresses and / or warpage and / or cycle time. In this way, the optimal temperature or temperature range for decomposition, and the optimal temperature or temperature range for foaming can be independently selected and set.

[0042] Chemical foaming agents are compounds that form low molecular gases (e.g., nitrogen, carbon dioxide, carbon monoxide, oxygen, ammonia, etc.) when decomposed. Embodiments of chemical foaming agents include azobisisobutyronitrile, diazoaminobenzene, sodium monocitrate, and oxybis(p-benzenesulfonyl)hydrazine. Chemical foaming agents of azo, hydrazine, and other nitrogen groups are preferred. Azodicarbonamide is a preferred embodiment of this category. Other embodiments include isocyanates and sodium bicarbonate for polyurethane (PU). The core layer of the first thermoplastic material comprising the chemical foaming agent can be easily manufactured, for example, by extrusion or calendering.

[0043] The invention can be used with any type of blowing agent. However, the greatest benefit can be obtained from the press according to the invention when making sandwich panels as described above using physical blowing agents, in particular swelling agents.

[0044] A core layer having a thermoplastic material including a blowing agent and at least one skin layer is used as the starting structure.

[0045] Thermoplastic materials suitable for the core layer to be foamed using a physical foaming agent include both crystalline thermoplastic materials and amorphous thermoplastic materials. In view of solubility, amorphous thermoplastic materials are preferred.

[0046] Thermoplastic materials suitable for the core layer foamed using a chemical blowing agent include both crystalline thermoplastic materials and amorphous thermoplastic materials. Crystalline thermoplastic materials are preferred because the temperature difference between the glass transition temperature and the melting point is small, providing the possibility of solidifying the thermoplastic material once foamed within a small temperature interval.

[0047] Thermoplastic materials, in particular fiber-reinforced thermoplastic materials, as well as metal sheets (e.g. aluminum) can be used as materials for the skin layer (also referred to as covering layer, facing layer or panel). The bottom covering layer and the top covering layer are preferably made of the same material, but a combination of a bottom covering layer of metal (e.g. aluminum) and a top covering layer of (fiber-reinforced) thermoplastic material is also considered, for example. The choice of the material for the core layer and the skin depends, among other things, on the desired properties of the final product application.

[0048] The thermoplastic materials used for the core layer and the cover layer can be the same or different, including different grades. In the following, for the purpose of indication, the thermoplastic material in the core layer is indicated as the first thermoplastic material, and the thermoplastic material in the cover layer (if any) is indicated as the second thermoplastic material. Embodiments include: polyetherimide (PEI), polyethersulfone (PES), polysulfone (PSU), polyphenylsulfone (PPSU), polyketones such as polyetheretherketone (PEEK), PPS polyphenylene sulfide, liquid crystal polymers, polycarbonate (PC), polyolefins (obtained from C1-C4 monomers) (such as polypropylene (PP)), polyvinyl chloride (PVC), polyethylene (PE), thermoplastic polyurethane (TPU), PA polyamide, PC polycarbonate, etc. and combinations thereof. It is also envisioned that combinations of different cover layers such as PEI / PEEK, PPSU / PEEK and PEI / PC are also contemplated. Also contemplated are thermoplastic biopolymers. It is also contemplated to use a mixture of, for example, PEI and PC in a fiber-reinforced face layer. The skin may comprise one or more sub-layers, the number of which may vary locally, for example to allow for locally specific additional reinforcements. In the case of locally different skins, the heat transfer properties (e.g. heat capacity and / or thermal conductivity) are generally also locally different. The press may then be equipped with non-adherent local compensation parts that equalize the heat transfer properties.

[0049] Advantageously, at least one skin is a fiber-reinforced layer of the second thermoplastic material.Preferably, both skins are fiber-reinforced layers of the second thermoplastic material.

[0050] As indicated above, combinations of different thermoplastic materials for the first thermoplastic material and the second thermoplastic material may also be used. Embodiments include PEI for at least one core layer, the at least one core layer being covered with a (fiber reinforced) skin made of PPSU, PS, PEEK or PC; PES or PPSU or a combination of PES and PPSU for the at least one core layer, the at least one core layer being covered with a (fiber reinforced) cover layer made of PSU (polysulfone) or PC; and PP for the at least one core layer, the at least one core layer being covered with a (fiber reinforced) layer made of polyamide, such as nylon.

[0051] In view of compatibility, advantageously, the type of the first thermoplastic material of the core is the same as the type of the second thermoplastic material in the face layer.

[0052] Glass fibers are the preferred reinforcement. Other inorganic fibers (such as metal fibers, carbon fibers) and organic fibers (such as aromatic polyamide fibers, polymer fibers, nanofibers of the above fibers and natural fibers) can be used in the same manner, provided that they can withstand the temperatures experienced during the operation of the method according to the invention. The fibers can be used in the form of mats, fabrics, cut fibers, etc. Advantageously, oriented fibers (especially unidirectional fibers) can also be used, in which the fiber direction has been adapted to the intended use. High-strength, high-elongation steel cords can be present in the fiber-reinforced covering layer. Particles such as metal nanoparticles or inorganic nanoparticles can be used to replace fiber reinforcement or as a supplement to fiber reinforcement.

[0053] It is also possible to apply reinforcement between the sub-layers of the core layer of thermoplastic material, in which chemical or physical foaming agents, in particular swelling agents, are incorporated. Examples of such reinforcements include (glass) fiber reinforced layers, metal layers, steel cords.

[0054] Another preferred embodiment of the starting structure is a mat made of both inorganic fibers and thermoplastic fibers, for example a mat made of glass fibers and acrylic fibers or inorganic fibers and thermoplastic powder.

[0055] Additives such as nucleating agents, plasticizers, melt strength improvers, and nanoparticles may also be present in the first thermoplastic layer.

[0056] The press plates of the press according to the invention may have a flat surface. It is also envisaged that one or both of the press plates have a 2D or 3D curved configuration.

[0057] The invention also relates to a method for producing a sandwich panel in a press having a press plate, in particular a press according to the invention, the sandwich structure comprising at least one foam layer having a first thermoplastic material and a cover layer, the method comprising the following steps:

[0058] a) providing a starting structure comprising at least one layer comprising a first thermoplastic material and two covering layers; wherein the at least one layer comprising the first thermoplastic material comprises a physical blowing agent;

[0059] b) contact-heating the starting structure between pressing tools of the press to a foaming temperature while maintaining pressure on the starting structure by the pressing tools;

[0060] c) foaming at least one layer of said first thermoplastic material comprising a physical foaming agent, advantageously according to a predetermined foaming curve, by moving said pressing tool a predetermined distance away, at said foaming temperature, while maintaining pressure on the foaming structure, wherein the volume is increased to a final volume and then kept constant, thereby obtaining said sandwich panel;

[0061] d) in a first cooling stage, cooling the sandwich panel to a first predetermined temperature of the press plate, such as below the glass transition temperature of the first thermoplastic material containing a physical blowing agent, for example in the range of about 110° C.-120° C., while in contact with the press plate and under pressure at a constant final volume, by opening the outlet pressure control valve and flowing temperature-controlled water from at least one water source (such as recycled water from a flash tank and / or a separate temperature-controlled water source) through at least one flow channel of the pressing tool to the outlet pressure control valve by means of a circulation pump, thereby converting water into steam;

[0062] e) optionally, in a second cooling stage, cooling the sandwich plate from the first predetermined temperature to a second predetermined temperature of the platen by causing temperature-controlled water from at least one water source (such as a combination of recycled water from a downstream flash tank and other temperature-controlled water) to flow at an increased flow rate through at least one flow channel of the platen by means of the circulation pump;

[0063] f) cooling the sandwich panel of step d) or optionally step e) from said second predetermined temperature to ambient temperature in a third cooling stage by flowing temperature-controlled water from at least one water source at a reduced cooling rate, advantageously at an increased flow rate; and

[0064] g) opening the press and removing the sandwich panel cooled in step f) from the press.

[0065] The physical blowing agent in the first thermoplastic material reduces the glass transition temperature of the first thermoplastic material. In the above step d), the glass transition temperature is the glass transition temperature of the first thermoplastic material containing the physical blowing agent. As a guide, the first predetermined temperature of the cooling step d) can be set to at least tens of degrees Celsius above the boiling point of the physical blowing agent, such as in the range of 20°C-40°C.

[0066] The invention also relates to a method for producing a sandwich panel in a press having a press plate, in particular a press according to the invention, the sandwich panel comprising a cover layer and at least one foam layer having a first thermoplastic material, the method comprising the following steps:

[0067] a) providing a starting structure comprising at least one layer comprising a first thermoplastic material and two covering layers; wherein the at least one layer comprising the first thermoplastic material comprises a chemical blowing agent having a decomposition temperature above the melting temperature or melting range of the first thermoplastic material;

[0068] b) heating said starting structure in contact between the platens of said press to a temperature above the decomposition temperature of said chemical foaming agent so that decomposition of said chemical foaming agent occurs, thereby obtaining an intermediate structure in which the decomposed chemical foaming agent is present in said at least one layer with said first thermoplastic material, while maintaining pressure on said starting structure by said platens;

[0069] c) cooling the intermediate structure obtained to the foaming temperature after decomposing the chemical foaming agent by opening an outlet pressure control valve and allowing temperature-controlled water from at least one water source (such as recycled water from a downstream flash tank) to flow through at least one flow channel of the pressing tool to the outlet pressure control valve by means of a circulation pump, the temperature and pressure of which are lower than the saturation pressure of the pressing plate at the current temperature, to convert the water into steam while the pressure on the intermediate structure is maintained by the pressing plate;

[0070] d) foaming said at least one layer of said first thermoplastic material comprising said decomposed chemical foaming agent, advantageously according to a predetermined foaming curve, at said foaming temperature, by moving said pressing plates a predetermined distance away, while applying pressure to the foamed structure, wherein the volume is increased to a final volume and then kept constant, thereby obtaining said sandwich panel;

[0071] e) in a first cooling stage, cooling the sandwich panel to a first predetermined temperature, e.g. below the glass transition temperature or melting temperature or melting range of the first thermoplastic material, such as a temperature in the range of about 110°C to 120°C, while being pressed in contact with the press plate, at a constant final volume by opening an outlet pressure control valve and flowing temperature-controlled water from at least one water source (such as recycled water from a downstream flash tank) through at least one flow channel of the pressing tool to the outlet pressure control valve by means of a circulation pump, thereby converting hot pressurized water, the temperature and pressure of which are below the saturation pressure of the press plate at the current temperature, to the press plate (at such first predetermined temperature below Tg or Tm, the foam cells are stable and retain their shape);

[0072] f) optionally, in a second cooling stage, cooling the sandwich plate from the first predetermined temperature to a second predetermined temperature by causing temperature-controlled water from at least one water source (such as recycled water from a downstream flash tank) to flow at an increased flow rate through at least one flow channel of the platen by means of the circulation pump;

[0073] g) cooling the sandwich panel of step e) or optionally step f) from said second predetermined temperature to ambient temperature in a third cooling stage by flowing temperature-controlled water from at least one water source; and

[0074] h) opening the press and removing the sandwich panel cooled in step g) from the press.

[0075] The method according to the invention, in which at least one cooling stage after foaming is performed by converting hot pressurized water into steam, has the same advantages as the press described above. The various advantageous and preferred embodiments of the press can also be applied in a similar manner to the method, including condensing the steam in a flash tank and reusing the condensed steam in the first cooling stage and / or in the second cooling stage.

[0076] For chemical blowing agents, the foaming temperature is above the glass transition temperature of amorphous thermoplastics and above the melting point or melting range of (semi)crystalline thermoplastics.

[0077] Foaming takes place under controlled pressure contact of the pressing plates with the starting structure, the pressing plates being moved away from each other. During foaming, the volume of the structure is increased to a final volume, in particular a final thickness, which is then kept constant, so that the sandwich panel is obtained. Due to the temperature difference between the operating temperature of the foaming step and the final low temperature (usually, the ambient temperature), a temperature-dependent volume reduction (contraction) may occur. In any case, no further expansion occurs. As explained above, the cooling step with phase change can be partially carried out under reduced pressure.

[0078] The present invention is further illustrated by the accompanying drawings, in which:

[0079] Figure 1 is a general diagram of an embodiment of a press according to the present invention; and

[0080] Figure 2 is a schematic diagram showing an embodiment of a press according to the invention in more detail.

[0081] In the drawings, similar components and parts are indicated by the same reference numerals.

[0082] exist Figure 1In the figures, one embodiment of a press for manufacturing sandwich panels is indicated as a whole by the reference numeral 10. The press 10 comprises two platens 12 and 14, respectively, which can be displaced relative to each other. For example, the lower platen 14 can have a fixed position, while the upper platen 12 can be displaced vertically (as indicated by arrow A), for example by means of a hydraulic cylinder (not shown). Each platen 12, 14 has at least one internal flow channel 16 in its body, which extends from an inlet 18 to an outlet 20. Typically, a plurality of internal flow channels are distributed in the body of each plate 12, 14 without compromising the strength of the platen beyond a critical value related to the pressure to be applied during operation. Arrow B indicates the flow direction of the fluid through the internal flow channel 16. It can be seen that in this embodiment adjacent flow channels are supplied in a counter-current manner. In Figure 1 The right side of FIG. 2 shows a finished sandwich panel 22 having two thin cover layers 24 and 26 and a thicker foam core 28. The cover layers 24 and 26 are advantageously layers of glass-fiber reinforced thermoplastic material, wherein the thermoplastic material is preferably the same as the thermoplastic material in the foam core 28.

[0083] Figure 2 An embodiment of a press 10 according to the invention is shown in more detail.

[0084] The flow passages 16 (shown in the figure for clarity) in each platen 12, 14 Figure 2 The inlet 18 of the heater 34 (only a few of which are shown in the drawing) is connected to a supply connection 30, and the outlet 20 is connected to a collector connection 32. A hot water outlet 36 of a heater 34 for generating hot fluid for heating the platens 12, 14 is connected to the supply connection 30 via a valve 37, through a fluid supply pipe 38 and a branch pipe 40. The heater 34 has a new fluid supply line 42 for introducing new fluid.

[0085] On the discharge side of the platens 12 and 14, the collector connection 32 is connected to the return inlet 48 of the heater 34 via a branch discharge conduit 50 and a return conduit 52 provided with a valve 54 and a pump 55, the return inlet 48 being provided with a valve 49. A discharge conduit 56 with an outlet pressure control valve 58 connects the return conduit 52 to a flash vessel 60 provided with an optional vacuum pump 62. A recovery conduit 63 connects the recovery water outlet 65 of the flash tank 60 to the return conduit 52 upstream (suction side) of the pump 55. The platens 12, 14 are provided with a temperature sensor 64 connected to a controller 66 (such as a PC or PLC), the controller 66 comprising a processor 68 and a memory 70 for controlling: the operation of the press (including opening and closing of the press), the conditions such as the temperature, pressure and flow of the pressurized hot water supplied, the hot fluid for (pre)heating and initial cooling, and the temperature-controlled water for further cooling, and the related equipment (such as heaters and valves).

[0086] The press operates as follows.

[0087] The starting structure comprises a core layer between skins. In one embodiment, the core layer consists of a thermoplastic material containing a physical blowing agent. The skins are advantageously glass fiber reinforced thermoplastic layers, wherein preferably the thermoplastic material is the same as the thermoplastic material in the core layer.

[0088] The starting structure is placed between preheated platens 12, 14 in a fitted manner at its periphery to prevent lateral (horizontal) expansion / foaming. A hot fluid is flowed through the fluid circulation loop (comprising the heater 34 and the platens 12, 14) using a pump 55, so that the platens 12 and 14 have been preheated to a foaming temperature depending on the thermoplastic material used, such as in the range of 170°C-190°C. The press 10 is closed so that both the platens 12 and 14 are in contact with the starting structure. The closing of the press 10 is performed quickly to prevent premature and uncontrolled foaming of the core layer of the starting structure containing the physical foaming agent before pressure is applied by the platens 12, 14. When a uniform foaming temperature of the starting structure is obtained (above the boiling point of the physical foaming agent), the distance between the platens 12, 14 is increased in a controlled manner so that the skins maintain their contact with the respective platens 12, 14, thereby also applying pressure during the foaming process. Once the distance has increased to its predetermined value, and thus the starting structure (particularly its core layer) has been foamed to a corresponding predetermined thickness, the circulation flow from the heater through the flow channel 16 is interrupted by operating the valves 37 and 54, and cooling begins. When the first cooling phase begins, the outlet pressure control valve 58 begins to open and maintains the circulation in the fluid circulation loop by the pump 55. Advantageously, on the upstream side of the platens 12, 14, the volume of the fluid circulation loop from the pump 55 is small, so that before the actual cooling begins, only a small amount of hot water with a high temperature for heating is present and needs to flow through the flow channel 16 of the heated platens 12, 14. The pressurized hot water contained in the circulation loop (whose temperature and pressure are lower than the saturation pressure of the platens 12, 14 at the current temperature) will expand and transform into steam at the outlet control pressure valve 58 and in the flash tank 60. If the flash tank 60 is kept at atmospheric pressure (without the reduced pressure applied by the vacuum pump 62), the recovered water will have a temperature of about 100°C. The recovered water is fed through the circulation conduit 63 by the pump 55, is pressurized at the pump 55, and then returns to the platens 12, 14, where it forms steam again and dissolves in water before being sent to the outlet pressure control valve 58. This type of evaporative cooling continues until the platens 12, 14 reach a first predetermined temperature. At this point, the temperature difference between the platens 12, 14 and the water temperature (about 100°C) is small, so that the cooling rate will slow down. In order to maintain a high cooling rate, a second cooling stage is optionally started, in which temperature-controlled water from the water reservoir 72 is introduced into the return conduit 52 at a position upstream of the pump 55 through the conduit 74 and the optional pump 76. The combined flow including the recovered water and the temperature-controlled water (having a temperature, for example, in the range of 70°C-90°C) is pressurized by the pump 55 and supplied to the platens 12, 14, causing the platens 12, 14 to be further cooled to a second predetermined temperature.At the end of the second cooling stage, the press plate is brought to a second predetermined temperature by water cooling (convection / conduction), after which the press switches to final cooling (third cooling stage) using temperature-controlled water from source 72 or other temperature-controlled water source (not shown) to cool the press plate from the second predetermined temperature to ambient temperature at a lower cooling rate.

[0089] In case a chemical blowing agent is used, the press is heated to a temperature above the decomposition temperature of the chemical blowing agent.

[0090] Typically, the platens 12 and 14 are preheated to a temperature well above the melting temperature or melting range of the thermoplastic material being used and above the decomposition temperature of the chemical blowing agent. Alternatively, the platens 12 and 14 are preheated to a temperature below the melting point of the thermoplastic material to be foamed and, therefore, below the decomposition temperature of the chemical blowing agent, which is above the melting temperature. After closing the press 10, the temperature of the starting structure is further increased by heating the platens 12, 14 to a temperature above the decomposition temperature. After the blowing agent decomposes, the structure is rapidly cooled to a suitable temperature above the melting point / melting range of the thermoplastic material by evaporative cooling via the outlet pressure control valve 58 as described above. Cooling is continued until a lower predetermined temperature above the melting temperature of the thermoplastic material is reached. When the starting structure, still under pressure, has reached a uniform temperature just above the melting temperature of the thermoplastic material used in the core layer, the distance between the pressure plates 12, 14 is increased in a controlled manner so that the skins maintain their contact with the respective pressure plates 12, 14, thereby maintaining pressure on the foamed structure. Once the distance has increased to its predetermined value so that the starting structure, in particular the core layer of the starting structure, has foamed to a corresponding predetermined thickness, cooling is restarted by operating the outlet pressure control valve 58 in the three cooling stages as described above. The intermediate cooling from the decomposition temperature to the melting temperature of the thermoplastic material can be omitted. Then, foaming is performed at a relatively high foaming temperature.

[0091] In the case of the embodiment with a vacuum pump, the second cooling stage is omitted.

Claims

1. A press (10) for producing sandwich products comprising a foamed thermoplastic core between cover layers, in particular a thermoplastic sandwich panel, more particularly for in situ production of a thermoplastic sandwich panel (22), said press (10) comprising: A first platen (12) and an opposing second platen (14) are configured to be movable relative to each other, each platen (12, 14) having at least one internal flow channel (16) having an inlet (18) and an outlet (20), wherein at least one of the platens (12, 14) is equipped with a temperature sensor (64), a heater (34) configured to produce hot water, the heater having a hot water outlet (36) provided with a valve (37), a return inlet (48) provided with a valve (49) and a fresh water supply inlet (42), A fluid circulation loop for heating and cooling the platens (12, 14) comprising: a fluid supply conduit (38) in fluid communication with the outlet (36) of the heater (34) and in fluid communication with the inlet (18) of the at least one internal flow channel (16) in each platen (12, 14), a fluid return conduit (52) in fluid communication with the outlet (20) of the at least one internal flow passage (16) of each platen (12, 14) and in fluid communication with the return inlet (48) of the heater (34), wherein the fluid return conduit (52) is in controlled fluid communication with an outlet control pressure valve (58), The fluid return pipe (52) is provided with a circulation pump (55) for pressurizing the water in the fluid circulation loop; at least one water source (60, 72) configured to supply temperature-controlled water, the at least one water source having an outlet in fluid communication with the fluid return conduit (52) upstream of the pump (55) and provided with a valve; A control device (66), the control device being configured to measure the current temperature of at least one platen (12, 14) through the temperature sensor (64), and to set the water flow rate in the fluid circulation loop through the circulation pump (55), and to open the outlet control pressure valve (58) during a first cooling stage of cooling the at least one platen to a first predetermined temperature, so that temperature-controlled water pressurized by the circulation pump (55) and having a temperature and a pressure lower than the saturation pressure of the platen (12, 14) at the current temperature is supplied from the at least one water source (72) through the fluid return pipe (52) to the platen (12, 14); and configured to allow temperature-controlled water from the at least one water source (72) having a temperature lower than the current temperature of the at least one platen (12, 14) to flow through the fluid circulation loop during a third cooling stage of cooling the at least one platen (10, 12) from a second predetermined temperature equal to or lower than the first predetermined temperature to ambient temperature at a reduced cooling rate.

2. A press according to claim 1, wherein the downstream side of the outlet control pressure valve (58) is at atmospheric pressure, wherein the control device (66) is also configured to introduce water from the at least one water source (72) into the fluid circulation loop during a second cooling stage of cooling the at least one press plate (12, 14) from a first predetermined temperature to a second predetermined temperature, and increase the total water flow by controlling the pump (55).

3. The press of claim 1 or claim 2, further comprising a vacuum pump (62) in fluid communication with the outlet control pressure valve (58), wherein the second predetermined temperature is equal to the first predetermined temperature.

4. A press according to claim 1 or claim 2, wherein the outlet control pressure valve (58) is in fluid communication with a downstream flash tank (60).

5. A press according to claim 4, wherein the at least one water source comprises the flash tank (60) and an additional water source (72), the flash tank (60) being provided with a water outlet fluidically connected to the fluid return pipe (52) upstream of the circulation pump (55), wherein the control device (66) is configured to circulate recovered water from the flash tank (60) to the fluid return pipe (52) during the first cooling stage, and the additional water source (72) is used to supply temperature-controlled water in the third cooling stage, has an outlet fluidically connected to the fluid return pipe (52) upstream of the pump (55) and is provided with a valve.

6. The press of claim 2, wherein the first predetermined temperature is in the range of 105°C - 125°C.

7. The press according to claim 2, wherein the second predetermined temperature is in the range of 75°C-90°C.

8. A press according to any one of the preceding claims, wherein the control device (66) is configured to control the temperature difference between the temperature of the cooling water and the temperature of the at least one press plate to be within a range below 15°C during the third cooling stage.

9. A press according to any one of the preceding claims, wherein the controller (66) is configured to control the outlet control pressure valve (58) so that the saturation pressure of water supplied to the press plate (12, 14) at the inlet pressure is equal to or lower than the saturation pressure of the press plate (12, 14) at the current temperature.

10. A press according to any one of the preceding claims, wherein the control device (66) comprises a processor (68) and a memory (70), the memory (70) storing computer readable instructions which, when executed by the processor (66), perform a process comprising: preheating the pressing tool (12, 14) by flowing hot fluid from the heater through the fluid circulation loop; closing the press (10) by moving the preheated press plates (12, 14) towards each other and applying pressure on the starting structure of the sandwich product (22) to be manufactured; heating the starting structure to a foaming temperature while applying pressure to the starting structure; causing the starting structure to foam at a foaming temperature by moving the pressing tools (12, 14) apart by a predetermined distance while maintaining pressure on the foaming structure; interrupting the flow of hot fluid from the heater (34) to the fluid circulation loop; In a first cooling stage, the outlet pressure control valve (58) is opened and temperature-controlled water from the at least one water source (60, 72) flows through the fluid circulation loop by means of the circulation pump (55), thereby cooling the press plate (12, 14) to a first predetermined temperature, wherein the temperature and pressure of the temperature-controlled water are lower than the saturation pressure of the press plate at the current temperature. Optionally, in a second cooling stage, the platens (12, 14) are cooled from the first predetermined temperature to a second predetermined temperature by flowing temperature-controlled water from the at least one water source (60, 72) at an increased water flow rate, And, in a third cooling stage, water cooling from the first predetermined temperature or the second predetermined temperature to ambient temperature is performed at a reduced cooling rate by flowing temperature-controlled water from the at least one water source (60, 72).

11. Method for producing a sandwich product (22) in a press having a press plate, preferably a press (10) according to any one of the preceding claims, the sandwich structure (22) comprising at least one foam layer (28) of a first thermoplastic material and a cover layer (24, 26), the method comprising the following steps: a) providing a starting structure comprising at least one layer comprising a first thermoplastic material and two covering layers; wherein the at least one layer comprising the first thermoplastic material comprises a physical blowing agent; b) contact-heating the starting structure between pressing tools (12, 14) of the press (10) to a foaming temperature while maintaining pressure on the starting structure by the pressing tools (12, 14); c) foaming the at least one layer of the first thermoplastic material comprising the physical foaming agent at the foaming temperature by moving the pressing tools (12, 14) apart by a predetermined distance while maintaining pressure on the foaming structure, wherein the volume is increased to a final volume and then kept constant, thereby obtaining the sandwich panel (22); d) in a first cooling stage, by opening an outlet pressure control valve (58) and allowing temperature-controlled water from at least one water source (60, 72) to flow through at least one flow channel (16) of the pressing tool (12, 14) to the outlet pressure control valve (58) by means of a circulation pump (55), thereby converting water into steam, wherein the temperature and pressure of the temperature-controlled water are lower than the saturation pressure of the pressing plate (12, 14) at the current temperature, and cooling the sandwich panel (22) to a first predetermined temperature of the pressing plate (12, 14) while in contact with the pressing plate (12, 14) under a constant final volume; e) optionally, in a second cooling stage, by means of the circulation pump (55), temperature-controlled water from the at least one water source (60, 72) flows at an increased flow rate through at least one flow channel (16) of the press plate (12, 14), cooling the sandwich panel from the first predetermined temperature to a second predetermined temperature of the press plate (12, 14); f) in a third cooling stage, cooling the sandwich panel (22) of step d) or optionally step e) from the first predetermined temperature or the second predetermined temperature to ambient temperature at a reduced cooling rate by flowing temperature-controlled water from the at least one water source (60, 72); as well as g) opening the press (10) and removing the sandwich panel (22) cooled in step f) from the press (10).

12. Method for producing a sandwich panel (22) comprising at least one foam layer (28) of a first thermoplastic material and a cover layer (24, 26) in a press having a press plate, preferably a press (10) according to any one of the preceding claims 1 to 10, the method comprising the following steps: a) providing a starting structure comprising at least one layer comprising a first thermoplastic material and two covering layers; wherein the at least one layer comprising the first thermoplastic material comprises a chemical blowing agent having a decomposition temperature above the melting temperature or melting range of the first thermoplastic material; b) heating the starting structure in contact between the platens (12, 14) of the press (10) to a temperature above the decomposition temperature of the chemical foaming agent so that decomposition of the chemical foaming agent occurs, thereby obtaining an intermediate structure, wherein the decomposed chemical foaming agent is present in the at least one layer with the first thermoplastic material, while maintaining pressure on the starting structure by the platens; c) after decomposing the chemical foaming agent, cooling the intermediate structure obtained to the foaming temperature by opening an outlet pressure control valve (58) and allowing temperature-controlled water from at least one water source (60, 72) to flow through at least one flow channel (16) of the pressing tool (12, 14) to the outlet pressure control valve (58) by means of a circulation pump (55), thereby converting water into steam, the temperature and pressure of which are lower than the saturation pressure of the pressing plates (12, 14) at the current temperature, while maintaining pressure on the intermediate structure by the pressing plates (12, 14); d) foaming the at least one layer of the first thermoplastic material comprising the decomposed chemical foaming agent by moving the press plates (12, 14) apart by a predetermined distance at the foaming temperature while applying pressure to the foamed structure, wherein the volume is increased to a final volume and then kept constant, thereby obtaining the sandwich panel (22); e) in a first cooling stage, by opening an outlet pressure control valve (58) and allowing temperature-controlled water from at least one water source (60, 72) to flow through at least one flow channel (16) of the pressing tool (12, 14) to the outlet pressure control valve (58) by means of a circulation pump (55), thereby converting hot pressurized water into steam, wherein the temperature and pressure of the temperature-controlled water are lower than the saturation pressure of the pressing plate (12, 14) at the current temperature, and cooling the sandwich panel (22) to a first predetermined temperature while being in contact with and pressurized with the pressing plate (12, 14) at a constant final volume; f) optionally, in a second cooling stage, causing temperature-controlled water from at least one water source (60, 72) to flow at an increased flow rate through at least one flow channel (16) of the press plate (12, 14) by means of the circulation pump (55) to cool the sandwich panel from the first predetermined temperature to a second predetermined temperature; g) cooling the sandwich panel (22) of step e) or optionally step f) from the second predetermined temperature to ambient temperature at a reduced cooling rate in a third cooling stage by flowing temperature-controlled water from the at least one water source (60, 72); as well as h) opening the press (10) and removing the sandwich panel (22) cooled in step g) from the press (10).

13. The method according to any one of the preceding claims 11 to 12, wherein the cooling step by converting hot pressurized water into steam is performed at sub-atmospheric pressure.

14. The method according to any one of the preceding claims 11 to 13, wherein the first cooling step by converting hot pressurized water into steam is performed with a continuous supply of water at a temperature of 80-100°C.

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