Method and device for producing rigid foam films

Abstract

The invention relates to a method for producing a rigid foam film, in particular for use as a core layer in sandwich composite elements, from a foam block (3) made of a thermoplastic, extruded, in particular partially crystalline and / or closed-cell plastic rigid foam material, in particular PET, which rigid foam film has a compressive strength that increases along the thickness extension extending perpendicularly to its surface.

Description

Technical Field

[0001] The invention relates to a method for producing a rigid foam film, in particular for use as a core layer in a sandwich composite element, from a foam block made of a thermoplastic, extruded, in particular partially crystallized and / or closed-cell PET plastic rigid foam material according to the preamble of claim 1, wherein the compressive strength extending perpendicularly to its surface, i.e. perpendicularly to the parallel side surfaces having the largest area compared to the other side surfaces (and therefore in the thickness direction) is higher than the compressive strength extending parallel to its surface, the method comprising the following steps: providing a foam block, the compressive strength of the plastic rigid foam material of which is higher along an axis of thickness extension (preferably the axis of extension of the thickness being the stretching axis or coinciding with the stretching axis) than in a surface extension extending perpendicularly to the axis of thickness extension. The invention relates to a method for producing a rigid foam film from a foam block, wherein the plastic rigid foam material of the foam block has a stretched polymer structure along the stretching axis; separating the film portion from the foam block to obtain (separate) the rigid foam film from the foam block by cutting the foam block along a feed axis extending perpendicular to the thickness extension axis using a knife having a cutting edge, the cutting edge preferably extending perpendicularly to the feed axis and perpendicular to the thickness extension axis, the film portion becoming longer along the feed axis during the duration of the cutting process; and lifting (i.e. deforming away) the separated film portion from the knife by elastic bending of the film portion, in particular about a feed axis extending perpendicularly to the thickness extension axis and the feed axis and therefore preferably extending parallel to the longitudinal extension of the cutting edge, in order to reduce the friction forces acting on the knife during the cutting process. As mentioned above, the rigid foam film is characterized by a higher compressive strength extending perpendicularly to its surface than parallel to its surface - assuming that the stretched polymer structure in the extrusion direction extending perpendicularly to the surface is the cause of the increased compressive strength.

[0002] For the purposes of the following description, unless otherwise specified, it is assumed that the plastic rigid foam material is a PET plastic rigid foam material.

[0003] In addition, the present invention relates to a rigid foam film according to claim 1, which is preferably produced by means of a method according to the invention, the film being made of a thermoplastic, extruded, in particular partially crystalline and / or closed-cell plastic rigid foam material, which has a polymer structure extending perpendicularly to the surface of the rigid foam film and thus stretched in the direction of its thickness extension, the rigid foam film having at least one surface side (preferably two parallel such surface sides) being obtained by a knife cutting process (in particular a cutting process without a heat element, such as a hot wire cutting process) and extending perpendicularly to the surface, i.e. a minimum thickness extension measured in the direction of the thickness extension axis of 0.5 mm, preferably 3 mm, more preferably 4 mm, particularly preferably 5 mm, and / or less than 10 cm, preferably less than 5 cm, more preferably less than 1 cm, particularly preferably 1 mm to 5 mm.

[0004] Furthermore, the invention relates to a sandwich composite element comprising such a rigid foam film according to claim 14 and to a rigid foam cutting device according to the preamble of claim 13 . Background Art

[0005] PET rigid foam films are known which are directly extruded with the desired thickness and have a polymer structure which is stretched in the extrusion direction and thus extends perpendicularly to the thickness, i.e. along the surface. The low compressive strength extending perpendicularly to the surface is disadvantageous, which makes such films less suitable as core layers in sandwich composite elements. Such PET rigid foam films are used in particular in thermoforming processes for forming containers, in particular in the form of trays for containing food.

[0006] Furthermore, it is known that flexible foams can generally be peeled without problems in all directions, regardless of any anisotropy of the mechanical properties.

[0007] Furthermore, for structural applications, in particular for use as core layers in sandwich composite elements, rigid foam films are already known which have a polymer structure which is stretched in the direction of its thickness extension, i.e. perpendicularly to its surface extension, for receiving relatively high compressive loads extending perpendicularly to its surface. Due to the associated high material losses, such rigid foam films are not obtained by sawing but by cutting with the aid of a knife from a foam block which can be produced, for example, as described in EP 1 536 944 B2. For this purpose, a rigid foam board is first obtained by extrusion which is divided into several main parts which are then connected to one another on their surface sides. If the foam block now obtained in this way is sliced ​​perpendicularly to the surface extension of the connecting surfaces, the slices have the desired polymer structure which has been stretched perpendicularly to their surface extension due to the extrusion process.

[0008] When using a knife to produce the above-mentioned slices or rigid foam films, the problem is that if no further measures are taken, the individual separated film parts will slide over the parts of the knife adjacent to the cutting edge and clamp the knife in this way. The friction forces thus generated will cause problems during the cutting process - in particular, the cutting process may stop, or the friction forces may prevent the knife from being displaced or moved perpendicular to the feed axis and perpendicular to the thickness extension axis as necessary for the cutting process. In addition, the heating of the knife will be too high, which is to be avoided to prevent the plastic foam material from melting and thus sealing the cutting surface of the rigid foam film. In order to avoid this friction problem, the corresponding film parts that have been separated from the remaining foam block by means of the knife are bent away from the knife, that is, lifted from the knife behind the cutting edge. This bending process is reversible, that is, elastic. However, in practice, the bending of the rigid foam film can only reach a very limited thickness extension of about 1mm. This method is not suitable for thicker rigid foam films - the rigid foam film breaks; for this reason, it is currently impossible to produce thicker rigid foam films with polymer structures that are stretched perpendicular to their surface extension by means of the knife cutting process. However, especially for industrial applications, the demand for such rigid foam films, especially rigid foam films having a thickness extension of at least 0.5 mm or more, would be high.

[0009] US 10065332 B2 relates to a device for splitting foam bodies, whereby layers are separated from the foam body by means of a band knife guided by or surrounded by a guide plate and transferred to a discharge device or removal device.

[0010] WO2016078902A1 relates to a method for planarly dividing PE, PP, PVC, PMMA or P(M)I rigid foam to obtain films or sheets, the rigid foam being first softened and then cut with a knife, the softening of the rigid foam before cutting being achieved by storing the rigid foam in water and / or heating or adjusting it to a temperature of at least 15°C and at most 1°C below the foaming temperature of the rigid foam. The present disclosure does not include any indication that PET plastic rigid foam materials can also be processed by means of this method. In addition, the foaming temperature of such rigid foam materials is usually significantly higher than the melting temperature or glass transition temperature.

[0011] EP1536944B2 relates to a planar structural element for the core layer of a sandwich composite element. DE102008046878B3 discloses a composite material with a PET foam core layer. DE102011084987A1 discloses a cutting machine with a rotating belt knife. Summary of the invention

[0012] Starting from the above-mentioned prior art, the object of the present invention is therefore to propose a method and a device by means of which a rigid foam film of substantially any thickness can be separated from a foam block by means of a knife, wherein the resulting rigid foam film has a higher compressive strength extending parallel to its thickness, i.e. perpendicular to its surface, than parallel to the surface. Furthermore, the object is to indicate such a rigid foam film and a sandwich composite element produced therefrom.

[0013] With regard to the method, the object is achieved by the features of claim 1; namely, in the overall method, the object is achieved by at least partially heating the plastic rigid foam material, in particular the foam block and / or the separated film part to a processing temperature above 40° C. and below the melting temperature of the plastic rigid foam material, so that the plastic rigid foam material (by heating) becomes elastically bendable so that the separated film part can be lifted off the knife (reversibly or elastically deformed) after passing through the cutting edge of the knife. The polymer molecular stretching axis preferably extends parallel to the rigid foam film dimension with the smallest extension, i.e. in the thickness extension direction. The compressive strength of the separated film part is highest in the thickness extension direction, i.e. higher than in the surface extension direction perpendicular to its extension.

[0014] Regarding the device, the object is achieved by the features of claim 16; that is, in a general rigid foam film cutting device, the object is achieved by providing a heating device, which is configured to at least partially heat the plastic rigid foam material, in particular the foam block and / or the separated film part to a processing temperature above 40°C and below the melting temperature of the plastic rigid foam material, so that the plastic rigid foam material becomes elastically bendable so that the separated film part can be lifted from the knife by elastic bending after passing through the cutting edge of the knife.

[0015] With regard to the rigid foam film, this object is achieved by the features of claim 13 , and with regard to the sandwich composite element, this object is achieved by the features of claim 14 .

[0016] Advantageous embodiments are described in the dependent claims. All combinations of at least two features disclosed in the description, the claims and / or the drawings form part of the scope of the invention.

[0017] In order to avoid repetition, the disclosed features related to the method are also considered to be related to the device, and thus can also be claimed. In the same way, the disclosed features related to the device are also considered to be related to the method, and thus can also be claimed.

[0018] The invention is based on the idea of ​​producing or ensuring elastic (reversible) deformation, i.e. bendability, of a plastic rigid foam material, in particular a foam block and / or an already separated film portion, in a general rigid foam film production method or a general rigid foam film cutting device by supplying thermal energy to a processing temperature above room temperature. The processing temperature is selected or the corresponding heating device is configured to heat the plastic rigid foam material to such a processing temperature that is above 40° C. and below the melting temperature of the plastic rigid foam, so that the plastic rigid foam material becomes so elastically bendable (compared to a room temperature of 22° C.) that the separated film portion can be lifted from the knife by elastic bending after passing through the cutting edge of the knife, in particular around a bending axis extending perpendicularly to the feed axis and the thickness extension axis. In other words, according to the invention, during a cutting process of a plastic rigid foam material with a knife in which the foam block and the knife are moved relative to each other on a feed axis (preferably extending perpendicularly to the longitudinal extension direction of the cutting edge of the knife), the plastic rigid foam material is heated (to a suitable processing temperature) so that the separated film portion, in particular even in the case of a thickness extension of at least 0.5 mm (measured perpendicularly to the surface extension of the film portion), becomes so elastically bendable that the separated film portion can be lifted or bent away from the in particular flat knife after passing through the cutting edge, thereby preventing or at least reducing friction effects on the knife. In the case of thick films, in particular those with a thickness of 2 mm or 3 mm or more, the required elastic bendability is generated or ensured only by the heating step to the processing temperature. Heating the plastic rigid foam material to the (increased) processing temperature not only contributes to the bendability obtained. In addition, the hardness of the material is reduced by the introduction of thermal energy, so that the knife can cut into the rigid foam plastic material better or more easily / with less resistance and the cutting pressure is reduced. After all, if the cutting pressure is too high, the knife will try to escape the pressure and move up and down, limited by a possible knife clamping, which can lead to "shocks" into the material. This can be avoided by heating. In addition, the risk of the knife being damaged by a significantly too high cutting pressure (knife pressure) is avoided. The foam block used in the method according to the invention is characterized in that it has a greater compressive strength in the direction of the thickness extension axis than in the direction perpendicular to the thickness extension axis, i.e. than along the feed axis and than along the longitudinal extension direction of the cutting edge of the knife used, i.e. than in the direction of the knife movement axis. Preferably, the increased compressive strength along the thickness extension axis is obtained or generated by stretching the polymer structure of the rigid foam material of the foam block along the thickness extension axis, which thickness extension axis then coincides with the stretching axis.

[0019] As will be explained below, different options are available with regard to the specific implementation of the heating step. For example, it is conceivable that in a corresponding environment, in particular in an oven, before and / or during the cutting process, the foam block is heated, in particular in its entirety, until the processing temperature is reached, which allows the separated film portion to be reversibly bent away from the knife, in particular in the case of a greater thickness extension of at least 0.5 mm, preferably at least 3 mm, particularly preferably at least 4 mm, more preferably at least 5 mm and / or less than 10 cm, preferably less than 5 cm, more preferably less than 1 cm. As an alternative to batch heating of the foam block in an oven, the foam block can be heated, in particular partially by heat radiation, in particular by means of IR radiators or infrared heating devices, preferably along the feed axis in front of and / or behind the foam block and / or in the contact area with the cutting edge of the knife. The advantage of this method is that the foam block does not have to be heated completely, but is essentially heated only on the surface to a depth corresponding to the thickness extension of the rigid foam film to be separated.

[0020] Therefore, an advantageous embodiment of the method provides that the heating is carried out by means of an infrared heating device which is adapted to the PET plastic rigid foam material in such a way that the penetration depth of the infrared radiation is at least equal to the thickness or thickness extension of the film portion to be separated or the rigid foam film to be separated. For the PET plastic rigid foam material, the appropriate choice of the infrared heating device has the following effect: the corresponding surface layer is quickly heated or heated up by a primary heat transfer with the foam block, i.e. not by thermal convection, i.e. directly after irradiation with infrared radiation, or at least faster than thermal convection, and the thickness or thickness extension of the layer corresponds at least to the layer thickness, thickness or thickness extension of the rigid foam film to be separated or the film portion to be separated. This ensures that even in the case of repeated partial heating of the foam block, in each case before the corresponding cutting process, a short heating is provided in the surface area of ​​the foam block while heating to a sufficient depth of thickness extension. For many PET plastic rigid foam materials, it has proven advantageous in this context that the infrared heating device has a short-wave proportion with a wavelength of 0.7 μm to 2 μm, which provides at least 20% of the radiation power, and the infrared heating device also has a long-wave proportion with a wavelength of more than 4 μm and which for its part does not provide or accounts for more than 35% of the radiation power. Such an infrared radiator or infrared heating device can have the effect that the penetration depth of the infrared radiation corresponds at least to the thickness extension of the rigid foam film to be separated or to the film part to be separated within the above-mentioned preferred thickness extension range, particularly preferably within the thickness extension range of the rigid foam film to be separated of up to 10 mm.

[0021] Furthermore, another particularly preferred embodiment of the method can provide that the surface temperature of the foam block is measured, preferably in a contactless manner, at a position arranged on the feed axis in front of the cutting edge and in front of the position where a heating device, in particular an infrared heating device, is arranged for heating, and the measured surface temperature is used as an input variable for controlling the radiant power of the heating device, in particular an infrared heating device. Said embodiment is based on the knowledge that too much heat input into the foam block can have a negative effect on the film portion to be separated or the rigid foam film to be separated. In particular, too much heat input can lead to undesirable ripples in the separated film portion; according to the current state of knowledge, said ripples are related on the one hand to the corresponding thermal expansion of the material and on the other hand to the limited expansion potential within the device. Thus, the controlled irradiation with thermal energy, in particular infrared radiation, ensures that on the one hand the surface of the foam block and the region of the foam block located below the surface have an elevated temperature, which allows the separated film or the separated film portion to be lifted advantageously, but at the same time the heat or heat input does not exceed an upper limit that leads to a reduction in the quality of the separated film portion.

[0022] More preferably, the surface temperature can be determined by means of a temperature sensor for contactless temperature measurement. For this purpose, for example, a pyrometer can be used. More preferably, the distance between the measuring position or measuring point of the surface temperature and the heating device, in particular the infrared heating device, and the selected feed rate are selected in the feed direction of the foam so that the time between the detection of the surface temperature via the generation of a corresponding control variable for influencing the radiant power of the heating device, in particular the infrared heating device, is selected in a manner related to the feed rate and taking into account the settling time or the setting time of the varying radiant power on the heating part of the heating device, so that when the corresponding area or corresponding part of the surface of the foam block enters the area of ​​heat radiation generated by the heating device, in particular the infrared heating device, a radiant power suitable for the measured surface temperature acts on the surface of the foam block. This ensures that a suitable radiant power is matched in each case to the measured surface or surface temperature. Thus, if the feed rate changes, the measuring point of the surface temperature can be changed, or if possible, the control variable for setting the radiant power of the heating device can be provided or transmitted to the heating device with a delay.

[0023] Therefore, in terms of the device, in addition to the corresponding temperature sensors, a control unit can advantageously be provided for controlling the radiation power of the heating device, in particular the infrared heating device, as a function of at least one control variable, in particular as a function of the measured surface temperature of the foam block, the surface temperature of the foam block being determined or measured at a position in front of the cutting edge and in front of the position of the heating device, in particular the infrared heating device, in the direction of the feed axis.

[0024] Furthermore, another particularly preferred embodiment of the method and the device can provide that a further temperature sensor measures the surface temperature of the foam block at a location downstream of the heating device, in particular the infrared heating device, with respect to the feed direction, the measured temperature being used and recorded, if applicable, only as a verification that the heat input to the foam block is sufficiently strong but not too great. Alternatively, however, the surface temperature of the foam block measured, preferably in a contactless manner, with respect to the feed axis and the feed direction, via a further temperature probe or a further temperature sensor after the heating device, in particular the infrared heating device, can also be used as a further control variable for controlling the radiant power of the heating device and can be supplied or made available to a corresponding control unit for this purpose.

[0025] In contrast to known thermal element cutting processes, in particular hot wire cutting processes, the knife is preferably one that has no current flowing through it and / or is not actively heated - the only temperature increase preferably results from mechanical friction effects and / or ambient temperature during the cutting process.

[0026] The cutting process is preferably carried out in such a way that not only the knife and the foam block are moved or displaced relative to each other along the feed axis, i.e. in particular perpendicularly to the longitudinal extension of the cutting edge in the foam block, but also a relative movement between the foam block and the knife perpendicularly to the feed axis and perpendicularly to the thickness extension axis is achieved, for example if the knife is implemented as a knife rotating in the rotational direction, in particular a band knife, in the form of a back and forth movement of the knife and / or the foam block along the above-mentioned knife movement axis or by driving the knife in the rotational direction. The latter option is preferred because in this case the knife designed as a rotating knife has sufficient time to cool down after cutting the contacting foam block before it contacts the rotating part again. Preferably, the temperature of the cutting area or the cutting edge area of ​​the knife does not exceed the melting temperature of the plastic rigid foam material during the cutting process in order to prevent sealing or partial sealing of the cut surface, i.e. the surface side of the rigid foam film.

[0027] In order to cut the (rigid) foam block in a particularly convenient and smooth manner, it has proven to be advantageous if the plastic rigid foam material, in particular the foam block and / or the separated film portion, is heated completely or partially to a processing temperature of 20° C., preferably 15° C., more preferably 10° C., particularly preferably 5° C., above the glass transition temperature of the plastic rigid foam material, and particularly preferably to a processing temperature above the glass transition temperature. In the case of rigid foam additives, in order to avoid collapse or destruction of the foam outside the immediate cutting area at temperatures already below the melting temperature of the rigid foam material, it has proven to be advantageous if the processing temperature is selected to be below 210° C., preferably below 180° C., more preferably below 150° C.

[0028] According to a first embodiment, the cutting edge of the knife is straight, ie without serrations. According to an alternative embodiment, the knife may also be serrated - it is important to minimize or avoid chip formation as much as possible.

[0029] The material thickness of the knife measured perpendicularly to the longitudinal extension of the cutting edge and perpendicularly to the cutting blade depth (which extends perpendicularly relative to the longitudinal extension of the cutting edge) is preferably selected from a value in the range of 0.5 mm to 3 mm and particularly preferably 1 mm. The effective cutting blade length is preferably selected to be longer than 0.5 m and particularly preferably selected from a value in the range of 0.9 m to 3 m, preferably 0.9 m to 2.5 m, more preferably 1 m to 2 m, even more preferably 1 m to 1.5 m. The knife depth measured in the feed direction of the knife relative to the foam block and extending perpendicularly to the material thickness and perpendicularly to the cutting blade length is preferably selected from a value in the range of 30 mm to 150 mm, particularly preferably 40 mm to 100 mm.

[0030] The elastic bending is particularly preferably carried out in such a (reversible) manner that, apart from the interaction of the plastic rigid foam material with the cutting edge of the knife, there is no plastic dimensional change, preferably no plastic shaping, of the rigid foam film during the cutting process, if applicable. In other words, the dimensions of the rigid foam film are not changed either along the thickness extension axis, nor along the feed axis, nor along the knife movement axis by the bending step and / or the heating step.

[0031] The cutting angle during cutting is preferably selected from a value in the range of 5° to 30°, in particular 8° to 20°.

[0032] It has proven particularly advantageous if the density of the foam block and / or the plastic rigid foam material and / or the rigid foam film is in the range of 40 kg / m 3 Up to 250kg / m 3 within the range.

[0033] In the context of the present invention, a rigid foam material according to DIN 7726 is a plastic foam material which has a compressive stress of more than 80 kPa at 10% compression. The plastic rigid foam material is particularly preferably characterized in that a cuboid with an edge length of 20 cm×2.5 cm×2.5 cm is wound around a cylinder with a diameter of 2.5 cm at a temperature between 15° C. and 25° C., i.e. at a constant winding speed of one revolution per 5 seconds according to standard ASTM D 1566-82, breaks.

[0034] The foam block is particularly preferably composed of a plurality of extruded main body segments, which are connected to each other on their contact surface sides, in particular welded and / or bonded, resulting in parallel or crossed reinforcement ribs when observing the surface side of the rigid foam film or foam block along the thickness extension axis of the polymer structure of the main body segment. With regard to an option of forming the foam block by welding, explicit reference is made to EP1536944B2, which is considered to belong to the present disclosure in this regard - here, the main body segments are welded to each other so that a reticular web structure with a reinforcing effect is produced by cross welds. Alternatively, in particular in the case of realizing a foam block with a small volume, the main body segments can be connected so that reinforcement webs, i.e. welds, are produced that do not cross but are only parallel to each other. If a welding process is realized, the welds, i.e. reinforcement webs, have few or no holes and preferably do not contain adhesive material. Alternatively, it is conceivable to produce parallel or crossed reinforcement webs by bonding the main body segments to each other - in principle, a combination of welding and adhesive processes is also conceivable, for example providing parallel welds and parallel bonding surfaces extending perpendicular to the parallel welds. It is also possible to use foam blocks without stiffening webs, the compressive strength of which is higher perpendicular to the surface than parallel to the surface.

[0035] The invention also relates to a rigid foam film, preferably produced according to the method of the invention. The rigid foam film is made of a thermoplastic, extruded, in particular partially crystalline and / or closed-cell plastic rigid foam material, which has a polymer structure that is stretched perpendicularly relative to the surface extension of the rigid foam film, the rigid foam film or at least one surface side extending perpendicularly to the thickness extension direction, preferably both surface sides (the surface with the largest surface extension) being obtained by a knife cutting process, in particular in such a way that no partial sealing of the surface side occurs or has already occurred due to the cutting process. The minimum thickness extension of the rigid foam film according to the invention is 2 mm, preferably 3 mm, particularly preferably 4 mm, particularly preferably 5 mm and / or less than 10 cm, preferably less than 5 cm, more preferably less than 1 cm, particularly preferably in the range of 1 mm to 5 mm.

[0036] Particularly preferably, the surface side with the largest surface extension has side edges extending perpendicularly to each other and having a respective minimum longitudinal extension of 50 cm. Preferably, the longitudinal extension of all side edges defining the surface side is selected to be a value ranging from 90 cm to 2.5 m, in particular from 1 m to 2 m, more preferably from 1 m to 1.5 m. Of course, the invention is not limited to such an embodiment. The method according to the invention can also be applied to very long or endless blocks, for example, in particular including the subsequent winding of separated film parts.

[0037] Furthermore, the invention relates to a sandwich composite element, at least one core layer of which is made of the rigid foam film according to the invention, which is sandwiched between at least two cover layers arranged on its surface sides and fixed to the core layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further advantages, features and details of the invention become apparent from the following description of preferred exemplary embodiments and from the accompanying drawings. In the drawings,

[0039] Figure 1 A partial diagram of a rigid foam film cutting device designed according to the concept of the present invention for performing the method according to the present invention is shown, wherein for the sake of clarity, a heating device is not shown.

[0040] Figure 2 Shown according to Figure 1 The device is arranged along a direction perpendicular to the feed axis V b and perpendicular to the thickness extension axis V s Extended knife moving axis M b Side view of

[0041] Figure 3 Shows Figure 2 A magnified view of the details of X,

[0042] Figure 4 Shown according to Figure 1 The device extends along the thickness direction V s Top view of the . DETAILED DESCRIPTION

[0043] In the figures, identical elements and elements having the same function are denoted by the same reference numerals.

[0044] Figures 1 to 4 Different views and partial enlarged details of a rigid foam film cutting device 1 designed according to the concept of the present invention are shown. The rigid foam film cutting device 1 comprises a cutting device 2 and a foam block 3 along a feed axis V shown. b Relative motion device for generating relative motion; in the exemplary embodiment shown, the foam block 3 consists only of plastic rigid foam material, in particular PET. Plastic rigid foam material is a thermoplastic, partially crystalline plastic material with closed cells and obtained by extrusion. During the extrusion process, the plastic material is subjected to high shear forces in the extruder with the help of a propellant gas and is extruded through a nozzle at the end of the extruder - downstream of the nozzle, the desired foaming process takes place by gas expansion. By the extrusion process, more precisely by extrusion through the nozzle, a polymer structure stretched in the extrusion direction is obtained. In the exemplary embodiment shown, the foam block 3 consists of a plurality of main body segments 4, which are welded (or optionally glued) to each other over their entire surface, and the reinforcing structure of, for example, cross reinforcing webs 5 has an axis V extending along the thickness. sAs will be explained below, the reinforcing web 5 consists of plastic melted by a welding process, or of an adhesive. As an alternative to the reinforcing structure of the cross reinforcing webs shown, completely parallel reinforcing webs or, for example, as in EP 1 536 944 B2 can also be realized. Figure 3 to the alternative geometry shown in Figure 8. For example, it is also possible not to implement reinforcing webs in order to produce a rigid foam membrane with a small surface.

[0045] Regardless of the specific arrangement of the main body segments or reinforcing webs, the foam block 3 or the plastic rigid foam material of the foam block has in any case a longitudinal direction perpendicular to the feed axis V. b and perpendicular to the knife moving axis M b Extended thickness Extended axis V s In other words, along the thickness extension axis V s The compressive strength is higher or greater than the thickness extension axis V s Vertical compressive strength.

[0046] In the exemplary embodiment shown, the knife 2 is realized as a band knife, which rotates in the direction of rotation U and moves in the region of the foam block 3 along the above-mentioned knife movement axis M. b relative to the foam block 3. The rigid foam film is produced in this way during the cutting process, wherein the foam block 3 and the knife 2 are displaced along the feed axis V b After passing the smooth cutting edge 7 of the knife 2, the corresponding separated film part 6 moves along the feed axis V b The cutting edge is parallel to the knife moving axis M b and perpendicular to the feed axis V b and thickness extension axis V s extend.

[0047] Figure 2 and Figure 3 The combined view of FIG. 1 shows that the separated membrane part 6 is bent away from the knife 2 by elastic bending about the bending axis A in the area behind the cutting edge 7 of the knife 2. The bending axis A is parallel to the knife movement axis M. b The elastic bending prevents the separated membrane section 6 from coming into contact with the blade side 8 facing away from the remaining foam block 6 on a large scale.

[0048] In order to first allow such elastic bending of the separated film part 6, the plastic rigid foam material is heated to a processing temperature by means of a heating device 9 (in the present embodiment in the form of an infrared radiator); at said processing temperature, the plastic rigid foam material does not melt, but can be elastically deformed so that the separated film part 6 can be lifted from the knife 2 as shown. In the present exemplary embodiment, the processing temperature is 80° C. In the exemplary embodiment shown, corresponding bending devices 10 in the form of ramps are provided for lifting the separated film part 6 and thus bending the separated film part 6 (see Figure 2 ).

[0049] Other heating devices can be implemented as an alternative to the infrared radiator - relatively thick rigid foam films, in particular parallel to the thickness extension axis V s A rigid foam film with an extended thickness extension d greater than 2 mm, the polymer structure of which is stretched in the thickness extension direction d, which can only be produced by heating the rigid foam material to processing temperature.

[0050] Figure 4 The device 1 according to the invention is shown in the feed axis V b The front part of knife 2 is located on the upper side. Figure 4 The top view along the thickness extension axis shows that the heating device 9 is arranged above the foam block 3, and the heating device 9 is designed as an infrared heating device. The infrared heating device includes separate heating devices 11, which are arranged with the feed axis V b At a certain angle to ensure uniform temperature rise or heating of the foam block 3 across the entire width of the foam block 3. In addition, Figure 4 The width of the heating device 9 is shown to be wider than the width of the foam block 3 , which also contributes to uniform heating of the foam block 3 over the entire width of the foam block 3 .

[0051] exist Figure 4 In the embodiment, a first temperature sensor 12 and a second temperature sensor 13 are provided, at least the first temperature sensor 12 being connected via a data connection to a control unit 14; the control unit 14 in turn being connected to the heating device 9 and being able to influence or control a controller of the heating device 9, in particular a controller of the heat output or radiant power of the heating device 9. Figure 4 In the embodiment, in addition to the corresponding connection between the first temperature sensor 12 and the control unit 14, another connection between the temperature sensor 13 and the control unit 14 can also be provided, so that the surface temperature of the foam block 3 measured by the temperature sensor 13 can also be provided to the control unit 14 as a control variable.

[0052] exist Figure 4 In the embodiment of the invention, the temperature sensors 12 and 13 are designed as pyrometers and extend along the thickness axis V sThe contactless measurement of the surface temperature of the foam block 3 is performed vertically downwards. However, other arrangements and measuring directions of the temperature sensors 12 and / or 13 may also be provided. Advantageously, however, the temperature sensor 12 is arranged or aligned in front of the heating device 9 along the feed axis, at least to the extent that during the time interval required for transmitting the measured surface temperature to the control unit 14, the respective surface temperature measured in the portion 15 of the foam block corresponding to the time interval in which the foam block has just covered a distance corresponding to the distance between the measuring position 15 and the position of the heating device 9 is used to generate a control variable for the heating device 9 and for adjusting the heating device 9 to a respective new or adapted radiant power. In other words, this means that the feed rate, the measuring position of the surface temperature and the inertia of the system are adapted to one another in such a way for setting the changed radiant power that an optimal adaptation of the radiant power to the measured surface temperature occurs.

[0053] The controlled radiation of the heat output of the heating device 9 ensures that, for example, after the separation of the film portion is introduced into the foam block, no excess heat energy is present which would have a negative impact on the film portion in the form of wave formation of the film portion. The heating device, in particular the infrared heating device, is adapted to the PET material or the PET plastic rigid foam material in such a way that the penetration depth of the infrared radiation and thus the direct or primary heating of the PET material is at least equal to the thickness extension or thickness of the film portion to be separated of the film or foam block to be separated. This ensures sufficient but not excessive heating over the entire layer thickness or thickness of the film portion to be separated, which on the one hand allows advantageous lifting of the separated film portion, but at the same time prevents excessive heating and thus negative impacts on the produced product, i.e. the separated film portion.

[0054] Reference numerals

[0055] 1 Rigid foam film cutting device

[0056] 2 Knives

[0057] 3 foam blocks

[0058] 4 Main body

[0059] 5 Strengthen the web

[0060] 6 Separated membrane fractions

[0061] 7 Cutting Edges

[0062] 8 Flat knife side

[0063] 9 Heating device

[0064] 10 Bending device

[0065] 12. First temperature sensor

[0066] 13 Second temperature sensor

[0067] 14 Control Unit

[0068] 15 Sections / measurement locations

[0069] V s Thickness extension axis

[0070] V b Feed axis

[0071] M s Knife moving axis

[0072] A Bending axis

[0073] d Thickness extension

[0074] U Circumferential direction

Claims

1. A method for producing a rigid foam film from a foam block (3), the foam block (3) being made of a thermoplastic extruded PET plastic rigid foam material, wherein the compressive strength extending perpendicularly to the surface of the rigid foam film is higher than the compressive strength extending parallel to the surface, the method comprising the following steps: - providing the foam block (3), the PET plastic rigid foam material of the foam block (3) extending along the thickness axis (V s ) has a higher compressive strength than the compressive strength perpendicular to the thickness extension axis (V s )’s compressive strength, - obtaining the rigid foam film from the foam block (3) by cutting the foam block (3) with the aid of a knife (2) having a longitudinal axis perpendicular to the thickness extension axis (V s ) extends along the feed axis (V b ) of the cutting edge (7), the film portion (6) is arranged along the feed axis (V b ) becomes longer during the cutting process, - lifting the separated film part (6) from the knife (2) by elastic bending of the separated film part (6) to reduce the friction forces acting on the knife (2) during the cutting process, It is characterized in that The PET plastic rigid foam material is at least partially heated to a processing temperature above 40° C. and below the melting temperature of the PET plastic rigid foam material, so that the PET plastic rigid foam material becomes elastically bendable, so that the separated film part (6) can be lifted from the knife (2) by elastic bending after passing the cutting edge (7) of the knife (2).

2. The method according to claim 1, characterized in that The rigid foam films are used in particular as core layers in sandwich composite elements.

3. The method according to claim 1, characterized in that The foam block (3) is made of a thermoplastic extruded, partially crystallized and / or closed-cell PET plastic rigid foam material.

4. The method according to claim 1, characterized in that: The foam block (3) and / or the separated film portion (6) are at least partially heated to a processing temperature above 40° C. and below the melting temperature of the PET plastic rigid foam material, so that the PET plastic rigid foam material becomes elastically bendable, so that the separated film portion (6) can be lifted from the knife (2) by elastic bending after passing through the cutting edge (7) of the knife (2).

5. The method according to claim 1, characterized in that The heating is carried out by means of an infrared heating device which is adapted to the PET plastic rigid foam material so that the penetration depth of the infrared radiation is at least equal to the thickness of the film portion (6) to be separated.

6. The method according to claim 1, characterized in that Measure the position of the feed axis (V b ) at a position on the surface temperature of the foam block, which is arranged in front of the cutting edge and in front of the position of the infrared heating device, and the measured surface temperature is used as an input variable for controlling the radiation power of the infrared heat source.

7. The method according to claim 6, characterized in that The surface temperature of the foam block was measured without contact.

8. The method according to claim 1, characterized in that The foam block (3) and / or the separated film part (6) are at least partially or completely heated to a temperature above the glass transition temperature of the PET plastic rigid foam material minus 20° C., and / or the foam block (3) and / or the separated film part (6) are at least partially or completely heated to a processing temperature below 180° C.

9. The method according to claim 1, characterized in that: The cutting process is performed such that the rigid foam film resulting from the cutting process has a minimum thickness extension (d) in the range of 0.5 mm to 10 cm, measured by extension perpendicular to the surface.

10. The method according to claim 1, characterized in that For cutting, the knife (2) moves along the knife movement axis (M b ) is moved relative to the foam block (3), or moves back and forth, and the knife movement axis (M b ) is perpendicular to the thickness extension axis (V s ) and perpendicular to the feed axis (V b ) extends, the knife (2) being in the form of a knife (2) rotating in a rotation direction (U).

11. The method according to claim 1, characterized in that: The knife (2) has no serrations at its cutting edge (7) and / or comprises a metal strip having a maximum material thickness having a value ranging from 1 mm to 5 mm.

12. The method according to claim 1, characterized in that The elastic bending takes place in such a way that, apart from the interaction with the cutting edge (7), if applicable, the cutting process does not lead to any plastic dimensional changes of the rigid foam film.

13. The method according to claim 1, characterized in that The density of the foam block (3) and / or the PET plastic rigid foam material and / or the rigid foam film is in the range of 40 kg / m 3 Up to 250kg / m 3 The value of .

14. The method according to claim 1, characterized in that According to DIN 7726, the rigid foam material has a compressive stress of more than 80 kPa at a compression of 10%.

15. The method according to claim 1, characterized in that The cutting edge (7) of the knife (2) is moved along the feed axis (V b ), in front of and / or in the contact area of ​​the cutting tool, before or during the cutting, the foam block (3) is heated to the processing temperature in an oven, or the foam block (3) is heated by thermal radiation.

16. The method according to any one of claims 1 to 15, characterized in that: The foam block (3) is composed of a plurality of extruded main body segments (4), which are welded and / or bonded to each other at their contact surface sides, and when extending along the thickness axis (V s ) When observing the surface side of the rigid foam film, parallel or intersecting reinforcement lines are formed.

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