DE102012023181A1 - Producing two-layer foam plates used for manufacturing rotor blades of wind turbines, comprises bonding two thinner foam sheets to a two-layer foam sheet, where adhesive is applied on one of surfaces of the thinner foam sheets - Google Patents

Abstract

The method comprises bonding two thinner foam sheets to a two-layer foam sheet. An adhesive is applied on one of surfaces of the thinner foam sheets. The amount of adhesive applied on the surface is 50-75%. The adhesive is point-shaped, line-shaped or grid-shaped on the surface of the thinner foam sheets. The adhesive is a dispersion glue or a hot melt adhesive. The hot melt adhesive is applied in molten state to the surface of the thinner foam sheets, where the application of the hot melt adhesive is uniform in a direction of the surface. The method comprises bonding two thinner foam sheets to a two-layer foam sheet. An adhesive is applied on one of surfaces of the thinner foam sheets. The amount of adhesive applied on the surface is 50-75%. The adhesive is point-shaped, line-shaped or grid-shaped on the surface of the thinner foam sheets. The adhesive is a dispersion glue or a hot melt adhesive. The hot melt adhesive is applied in molten state to the surface of the thinner foam sheets, where the application of the hot melt adhesive is uniform in a direction of the surface. Each surface to be bonded to the thinner foam sheets is foamable. A surface area of the applied adhesive in the surface is 20-400 g/m 2>. A width of a structural unit of the applied adhesive is 5-50 mm, and/or a distance between the individual structural units of the patterned applied adhesive is 5-50 mm. The method further comprises: drying the thinner foam sheets; treating the dried thinner foam sheets with electromagnetic radiation; joining the thinner foam plates on the surfaces to be bonded; and pressing the joined thinner foam sheets, and then optionally curing.

Description

The present invention relates to a method for producing at least two-layer foam sheets by bonding at least two thinner foam sheets, wherein on at least one surface of at least one thinner foam sheet at least one adhesive, for example a hot melt adhesive, is applied in a structured manner. As a result, 20 to 90% of the respective plate surface are provided with adhesive structured on the corresponding thinner foam plate. Furthermore, the present invention relates to the foam sheets as such, which are at least two-ply. The number of layers of the foam sheet as such results from the number of thinner foam sheets which are glued together. For example, when three thinner foam sheets are bonded together, a three-layer foam sheet is obtained as such, in the case of four thinner foam sheets, therefore, a four-layer foam sheet as such is obtained.

EP-A 1 318 164 relates to a process for producing thick extruded polystyrene foam boards (XPS boards) by joining two or more thin boards. The thick plates are obtained by uniformly wetting the thin plates at the surfaces where they are to be joined with an organic solvent for polystyrene. As a result, the foam surface is dissolved and the plates can then be pressed together. Suitable solvents are, for example, hydrocarbons, alcohols or ethers which have a boiling point between 50 and 250 ° C. Furthermore, in the method according to EP-A 1318 164 the foaming skins are peeled on the major surfaces of the plates to be joined together before they are wetted with the solvent.

EP-A 1 213 119 discloses a method for joining at least two thermoplastic resin foam starting sheets to a new sheet, wherein the starting sheets are extrusion skinless at the mating surfaces, and the source sheets are bonded by fusion welding. For solvent welding organic solvents are used which have a boiling point <150 ° C, for example acetone or mixtures of organic solvents with water.

EP-A 1 566 400 discloses foam panels having a coating on at least one panel surface, the coating including a polymeric film having a glass transition temperature in the range of -60 to + 40 ° C. The foam sheets may be, for example, a particle foam of polystyrene or polyolefin. The polymer film is formed on the foam sheets by applying a corresponding polymer dispersion to the foam sheets, which is then allowed to dry. The polymer dispersion or the polymer film resulting therefrom as a coating usually contains an amorphous, thermoplastic polymer, preferably a styrene-containing polymers such as styrene-acrylates and styrene-butadiene copolymers are used. The polymer dispersion may also contain numerous other substances such as fillers, flame retardants or infrared (IR) absorbing solids. These foam boards are suitable for the adhesion of mortar, concrete and plaster systems, in particular, they are used as a thermal insulation material in construction. EP-A 1 566 400 however, does not disclose that a plurality of individual such foam sheets can be assembled into a multi-ply thicker foam sheet. Nor is it disclosed therein that the polymer dispersions used are adhesives which can be applied in a structured manner to the surface of a foam board.

Extruded plastic foam sheets of great thickness are used in DE-A 101 063 341 disclosed. With the method described for connecting at least two plastic foam starting plates to a new plate, it is possible to produce plates with a minimum thickness of 70 mm. Preferably, these are fluorochlorohydrocarbon-free polystyrene foam boards. In the process, the starting plates, which are non-extrusion-free at the contact surface, are bonded together using a diffusion-open adhesive or mechanical fasteners. Alternatively, the method can also be carried out in such a way that a non-diffusible adhesive or only a slightly diffusible adhesive is used in the case of partial area connection and spotwise welding or spotwise adhesion. As polystyrene foam boards are particularly suitable XPS boards. In DE-A 101 063 341 However, there is no information as to which specific chemical composition the adhesives used, which may also comprise reaction adhesives and / or hot-melt adhesives, or whether the adhesives used can be applied in a structured manner to the surface of a foam board.

Another method for joining at least two plastic foam board starting sheets to a new sheet, which is preferably a polystyrene foam sheet having a minimum thickness of 70 mm, is disclosed in U.S. Pat EP-A 1 471 125 disclosed. In this process also starting plates are used, which are at least at the contact surface extrusion skinless, and there is a connection of the starting plates with a diffusion-open adhesive, wherein a hot-melt adhesive and / or reaction adhesive is used. The adhesive consists of isocyanate and at least one other reaction group, which is a resin which is tacky in the molten state and gives the adhesive bond an early strength. The isocyanate and the resin thereby react to polyurethane, whereby the adhesive effect is achieved with a final strength. Also in EP-A 1 471 125 There are no indications as to whether the adhesives used can be applied in a structured manner to the surface of a foam board.

Thermal insulation materials made of XPS composite materials, which are three-layered, are incorporated in WO 2012/016991 described. The three-ply nature of the composite materials results from combining lower, central, and upper XPS panels into the XPS composite, with each outboard side of this XPS composite comprising an extrusion skin. While the contact faces of the central XPS panel also have an extrusion skin, it is removed at the corresponding contact faces of the upper and lower XPS panels. The individual XPS panels are joined to the XPS composite material by thermal welding to the contact surfaces. WO 2012/016991 contains no information as to whether, alternatively or in addition to welding, adhesives may optionally be used in conjunction with flame retardants.

WO 2009/047487 discloses multilayer composite materials comprising a first layer of a closed cell foam of a thermoplastic and a second layer of a fiber reinforced resin deposited on the surface of the first layer. The closed-cell foam has a mean cell size of less than 100 microns, preferably it is a mixture of polystyrene and polyphenylene oxide (PS / PPO). These layered composite materials are suitable for producing larger structures, for example for wind turbine rotor blades.

A fundamental problem in gluing is the flammability and the performance of fire tests. Even if one takes into account that the to be bonded thinner plates and / or the adhesive itself are not or only very difficult to burn, a statement does not automatically apply to the product obtained, so the two- or multi-layer plates with a (compared to the thinner Output plates) of greater thickness. This different fire behavior is due to the formation of the so-called adhesive seam (also referred to as adhesive skin or adhesive layer) during the gluing process. The adhesive seam forms at the points where the surfaces of the thinner plates used are glued together. Depending on the presence or the thickness of the adhesive seam, the fire test B2 (in accordance with FIG DIN 4102 respectively. DIN EN ISO 11925-2: 2011-02 ) or not. The larger or thicker the adhesive seam, the higher the flames burn. This negative burning behavior (compared to the thinner starting plates) of the two-layered or multi-layered plates due to the presence of an adhesive seam is also referred to as the "wicking effect" which occurs at the boundary layer of the adhesive used to the thinner starting plate used. If, on the other hand, there is no adhesive seam or only a very thin adhesive seam, the respective thinner plates are not connected firmly enough so that the corresponding product is not stable.

The object underlying the present invention is to provide new two- or multi-layer foam boards as such or a corresponding method for producing such at least two-layer foam boards.

Is solved for the task by a method for producing at least two-layer foam boards by bonding at least two thinner foam sheets to the at least two-layer foam board, characterized in that on at least one surface of at least one thinner foam plate at least one adhesive is applied structured, wherein on the Surface of the thinner foam board, on which the adhesive is applied structured, 20 to 90% of the respective plate surface are provided with adhesive.

The at least two-ply foam sheets produced by the method according to the invention are characterized in that the corresponding number of thinner foam sheets can be glued or joined in a very stable manner to the at least two-ply foam sheets and in particular have improved properties with respect to their flame behavior. The improvement of the flame behavior (flame retardance) is not at the expense of the adhesive effect.

Preferably, the at least two-layer foam boards according to the invention (as such) pass the fire test B2 (according to FIG DIN 4102 respectively. DIN EN ISO 11925-2: 2011-02 )). This means that in the context of the present invention, the wicking effect, in particular during fire test B2, can be avoided, so that in the inventive at least two-layer foam boards the adhesive seam withstands the fire test according to fire test B2. By deliberately interrupting the adhesive seam (For example, by points, lines or grid) thus the fire zone is deliberately interrupted, so that the wicking effect does not come about. The at least two-layer foam boards as such furthermore have a high tensile strength, preferably a tensile strength of> 0.15 N / mm ² .

If the method according to the invention is carried out using hotmelt adhesives, in particular using the special hotmelt adhesives (defined below) which comprise at least one polymer (P1), the effects described above with regard to improving the flame behavior can be further enhanced. In this embodiment, preferably at a temperature of 70 ° C, a tensile strength of> 0.15 N / mm ^{2 is} obtained.

The stable assembly of the individual thinner foam boards according to the invention by gluing using adhesives, such as hot melt adhesive, optionally in conjunction with the additional use of components such as flame retardants. It is therefore not necessary that the individual thinner foam sheets are joined or glued together with the aid of a solvent (solvent welding) or by thermal welding. In the context of the present invention, however, in addition to the use of the adhesives, a thermal bonding step (by irradiation with electromagnetic radiation and optionally with the additional use of a corresponding absorber of electromagnetic radiation) may be performed to further enhance the cohesiveness of the individual thinner foam panels increase.

If an absorber of electromagnetic radiation together with at least one adhesive, in particular in the form of an aqueous adhesive dispersion, is applied to the thinner foam boards, a faster drying of the adhesive is observed as a result of the presence of the absorber or, where appropriate, the performance of the thermal welding, which is another Advantage represents. Due to the presence of the absorber, the adhesive can absorb much faster energy, resulting in faster drying and possibly better adhesive behavior.

Due to the presence of the absorber for electromagnetic radiation, the thermal welding to be carried out (in addition to bonding) also causes only the surface of the corresponding thinner foam sheet provided with the absorber to be selectively heated. Consequently, no holes are burned in the plate body during bonding / welding or this takes place only to an extremely small extent. This has the consequence that the corresponding thinner foam boards are not distorted during bonding in conjunction with the thermal welding, so that a precise adhesion of the individual thinner thermoplastic foam panels is observed, which in turn has a positive effect on the strength of the at least two-layer foam boards.

A particularly firm adhesion of the thinner foam sheets to be bonded together is then determined within the scope of the method according to the invention if at least one of the surfaces to be bonded of the thinner foam sheets is foam-free (also referred to as foam-free). In particular, this is to be determined if the surface to be bonded of the two thinner foam boards is foam-free for each pair of boards to be bonded. By removing the foam skin, a plate surface is produced, which can better absorb the adhesive and consequently is better to bond compared to foam plates, in which the foam skin (extrusion skin) has not been removed. Foam boards with foam skin have a much smoother surface, which, however, is usually not plane-parallel with the surface of the second plate to be bonded. As a result, warping of the panels during the bonding process is often observed, possibly resulting in reduced cohesion / reduced strength of the at least two-ply foam panels after bonding.

Furthermore, a particularly firm adhesion - in conjunction with an improved flame behavior - the thinner foam sheets to be bonded together in the process of the invention is then determined if the order of the adhesives used, especially in hot melt adhesive, especially in the special hot melt adhesives, the at least one polymer (P1), under "prestressing", especially when applied to foam skin-free surfaces. An application under bias in the context of the present invention means that the corresponding hot-melt adhesive is applied uniformly in one direction (for example the x-direction) of the respective plate surface of the thinner foam sheets to be bonded, taking into account the intended structure. As a result, first a pre-orientation / pre-orientation of the macromolecules is achieved both by the hotmelt adhesive and by the foam board.

Subsequently, the invention at least two-ply foam boards as such and the manufacturing method of this invention foam boards are defined by structured bonding closer.

The foam sheet according to the invention is at least two layers, so it can have exactly two layers or be three-ply, four-ply, five-ply or even higher ply. As already stated above, the number of layers of the foam sheet as such results from the number of thinner foam sheets which are glued together. In the case of a two-ply foam board as such, therefore, two thinner foam boards are glued together. In a three- or four-layer foam board as such, three or four thinner foam boards are thus glued together. If even higher-ply foam boards are to be produced as such, for example a ten-ply foam board, the number of layers corresponding number of thinner foam boards, for example, ten thinner foam boards must be glued together accordingly. The foam sheet according to the invention is preferably two-ply, three-ply or four-ply, in particular the foam sheet according to the invention is two-ply.

With regard to their chemical composition, the thinner foam boards used for bonding correspond to the at least two-layer foam boards produced as part of the process according to the invention (without taking into account the adhesives applied to the surfaces during the bonding process and any optional applied components such as flame retardants, binders, absorbers of electromagnetic radiation Etc.). The thinner foam sheets to be bonded together preferably have the same dimensions and / or the same chemical composition. Optionally, but also foam plates with different dimensions and / or different chemical composition can be glued together. For example, if three thinner foam sheets are glued together, all of which have the same sizing and are (for example) an extruded polystyrene foam (XPS foam), a three-ply extruded polystyrene foam (XPS) is thereby obtained.

The dimensioning of the thinner foam sheets to be bonded together is arbitrary. With regard to their length and width, they can measure in the centimeter range up to several meters. With regard to the third dimension (thickness), theoretically any dimensions are also conceivable; in practice, the thinner foam sheets have a thickness of 10 to 150 mm. The thickness of the at least two-layer foam boards produced in the process according to the invention thus results from the total thickness of the thinner foam boards used overall. In particular, if a pressing step is carried out in the context of the production method, the thickness of the at least two-layer foam sheets as such is less than the sum of the respective thicknesses of the thinner foam sheets used.

The thinner foam boards used for bonding as such are known in principle to the person skilled in the art. Suitable foam boards are for example in EP-A 1 566 490 or in the form of blends in WO 2009/047487 disclosed.

Preferably, the thinner foam sheets are a particle foam or an extrusion foam. Furthermore, it is preferred that the thinner foam sheets have a density <200 g / l. Furthermore, it is preferred that the thinner foam sheets are thinner thermoplastic foam sheets. This applies in particular to the case described below in that, in addition to bonding, thermal welding is carried out and / or the dried, thinner foam panels are activated by electromagnetic radiation.

More preferably, the thinner foam sheets are an extrusion foam, preferably a thermoplastic extrusion foam. The extrusion foam is preferably a polystyrene or styrene-made copolymer. Optionally, mixtures of such polymers can be used. More preferably, the extruded foam is extruded polystyrene (XPS), which is commercially available for example under the name styrodur ^® from BASF SE.

If the extrusion foam is based on (at least) one styrene copolymer (also referred to as styrene copolymers), this means that in addition to the monomer styrene at least one further monomer is required for the preparation of this copolymer. Preferably, this copolymer is prepared from styrene and another monomer. In principle, all styrene-polymerizable monomers are suitable as comonomers of styrene. Preferably, at least 50% by weight of styrene are copolymerized in this copolymer.

Preferably, a styrene-made copolymer as a comonomer to styrene has a monomer selected from α-methylstyrene, ring-halogenated styrenes, nuclear-alkylated styrenes, acrylonitrile, acrylic acid esters, methacrylic acid esters, N-vinyl compounds, maleic anhydride, butadiene, divinylbenzene or butanediol diacrylate. Acrylic acid esters and methacrylic acid esters are preferably obtainable from alcohols having 1 to 8 carbon atoms. A suitable N-vinyl compound is, for example, vinylcarbazole. Preferred copolymers prepared from styrene are styrene-acrylonitrile copolymers (SAN) or acrylonitrile-butadiene-styrene copolymers (ABS).

As adhesives, in principle, all adhesives known to those skilled in the art can be used, for example, the adhesives (adhesives) listed below are used in the present invention.

Basically, as adhesives for bonding the thin foam boards, in particular extruded polystyrene, solvent-free and aqueous adhesives are suitable. Solvent-based adhesives are less well suited for reasons of occupational safety and explosion protection, but can also be used. Solvents can additionally attack the polystyrene foam.

For solvent-free adhesives, 100% reactive adhesives (reactive adhesives) are preferred, especially one- and two-component polyurethane adhesives. In one embodiment of the present invention, a one- or two-component polyurethane adhesive is used as the adhesive (reactive adhesive).

Reactive cyanoacrylate ("superglue"), however, are less well suited, since they can be controlled worse in their setting time and are only partially suitable for bonding large areas.

Two-component acrylate structure adhesives are possible, but less preferred because of the problematic handling. One-component, moisture-curing acrylate compounds, as used in the EP A 1879974 can also be used, but are less preferred because of the long cure time. Two-component epoxy adhesives can be used, but their water vapor permeability is worse than less tightly crosslinked adhesives.

Hot melt adhesives (hot melt adhesives) are well suited. In the case of hotmelt adhesives, the application is preferably carried out under such gentle conditions that the foam is not exposed to high temperatures. Particularly preferred hotmelt adhesives are further characterized in that the application takes place at temperatures of 80.degree. C. to 160.degree. C., preferably of 85.degree. C. to 130.degree. C. In one embodiment of the present invention, polyurethane hotmelt adhesives (PU hotmelt adhesives) are preferred. It is particularly preferred that the hotmelt adhesive contains at least one polyurethane with isocyanate end groups, wherein the isocyanate end groups can preferably cure and / or crosslink after joining the file with air humidity or added water. This hot melt adhesive is also referred to as a moisture-curing polyurethane hot melt adhesive.

Furthermore, in one embodiment, hot melt adhesives are preferred which are defined by the hot melt adhesive comprising at least one polymer (P1) selected from the group of polyolefins, polyesters, polyamides, polyacrylates, styrene-isoprene copolymers, styrene Butadiene copolymers, ethylene-vinyl acetate copolymers or polyvinyl acetate (PVA).

In a further embodiment of the present invention, a mixture is used which comprises a hot-melt adhesive comprising at least one polymer (P1) and a moisture-curing polyurethane hotmelt adhesive.

In another embodiment of the present invention, the adhesive is a dispersion adhesive. Preferably, this adhesive is used in the context of the present invention as an aqueous dispersion.

Contact adhesives and laminating adhesives are particularly suitable for (aqueous) dispersion adhesives.

In the case of contact adhesives, dispersions based on polychloroprene, polyacrylate, styrene-acrylate copolymers and / or polyurethane are possible.

Laminating adhesives based on aqueous polyurethanes and / or polyacrylates are preferred.

In the case of (aqueous) laminating adhesives, drying and thermal activation are generally necessary after application of the adhesive. Preferably, the adhesive is applied to both sides and dried and then activated and pressed.

The (aqueous) dispersion adhesive is particularly preferably a contact adhesive or laminating adhesive based on a dispersion of polyacrylate, styrene-acrylate copolymers or polyurethane.

Pure pressure-sensitive adhesives can also be used, but rather in the lower range of the desired tensile strengths. They are slightly better if they are added to a crosslinker, which causes a solidification of the material after bonding.

Aqueous adhesives that physically dry after being added are useful, but require a longer time to reach ultimate strength. Such systems can also be used paste-like as low-viscosity or thickened unfilled glues or filled with fillers.

In the case of dispersion adhesives, it is optionally additionally possible to use a hardener, which may have an advantageous effect on the heat resistance and / or the resistance to hydrolysis.

In the process according to the invention, at least one adhesive is applied in a structured manner to at least one surface of at least one thinner foam sheet, wherein 20 to 90% of the respective sheet surface is provided with adhesive on the surface of the thinner foam sheet to which the adhesive is applied in a structured manner.

In the context of the present invention, the adhesive is structured, preferably punctiform, linear or latticed, in particular latticed, applied to at least one surface of at least one thinner foam board. This order form of an adhesive is also referred to as structured bonding and explained in more detail below.

The structured bonding with the adhesive can be done by any structures or structural forms. According to the invention, 20 to 90%, preferably 40 to 80%, in particular 50 to 75%, of the respective plate surface is provided with hotmelt adhesive on the surface of the thinner foam board, to which the adhesive is applied in a structured manner.

In the context of the present invention, the structures may also be referred to as patterns or structuring patterns. A structure is made up of at least one structural form, which may also be referred to as a structural unit. In the context of the present invention, a structural unit (structural form) is understood to mean the smallest unit in a pattern (structure). Such a structural unit may, for example, be a check, a rhombus, a rectangle, a cross, a square or a line. Optionally, such structural units can alternate or be combined with one another. Thus, patterns are conceivable which are constructed from a plurality of different structural units, for example from a plurality of lines of different thickness (width) and / or depth, which alternate, for example, with diamonds or squares. Thus, also in a grid, different structural units may be included, for example, squares of different sizes, which are arranged alternately. Such structures are also called rasters. For example, a grid can also be formed from several crosses. Such a structure, in the context of the present invention, represents an embodiment of a grid.

The distances between the individual structural units on the respective surface of the thinner foam board, which were produced by the application of the adhesive so, can take any values (sizes). Preferably, the distance between the individual structural units of the structured applied adhesive is 5 to 50 mm (average over the entire pattern), in particular, the distance is 7.5 to 20 mm. The width of a structural unit (structure), for example, the diameter of a dot (in a dot-shaped structure) or the width of a line (in a line or lattice-shaped structure) may be arbitrary, preferably in the range of 1 to 100 mm, more preferably 5 to 50 mm, in particular 10 to 25 mm.

In the context of the present invention, a structure (pattern) preferably contains at least five, more preferably at least ten structural units (structural forms). The upper limit of the number of structural units is in principle arbitrary, but depends on the plate size in conjunction with the size of a single structural unit and the upper limit of per plate with adhesive surface. As a rule, an upper limit of 50 structural units is not exceeded. In the case of points and lines, the corresponding structural units are not connected to each other; in the case of grids, in particular grids, the individual structural units can also be linked to one another, preferably they are arranged completely or at least partially isolated from one another. The individual structural units of a pattern may be the same or different, preferably they are the same (for example a pattern of a total of ten identical points, lines or crosses). Particularly preferably, the individual structural units of a pattern are arranged at the same distance from each other.

If, in this embodiment of the present invention, the adhesive per plate pair is to be applied to both surfaces of the thinner foam sheets to be bonded together, it is preferred that the two surfaces to be bonded have identical or at least 80% matching patterning patterns (pattern or structure). The two surfaces to be bonded preferably have identical patterning patterns. Furthermore, it is preferred that the surfaces to be bonded are superimposed prior to bonding in such a way that as many of the structures produced with the adhesive come to coincide with one another on both surfaces to be bonded. Particularly preferred in this embodiment of this embodiment, two surfaces are glued together with identical structuring pattern, wherein the surfaces to be bonded are superimposed prior to bonding so that the structures generated by the adhesive to both bonding surfaces completely coincide with each other.

Preferably, at least one adhesive is applied to only one bonding surface of the thinner foam sheets per pair of plates to be bonded. The application of the adhesive can be carried out by the usual methods, for example by brushing, spraying, rolling, knife coating or printing. The applied amount of adhesive is generally between 10 g / m ² to 400 g / m ² (solid), preferably 20 g / m ² to 200 g / m ² , more preferably 50 g / m ² to 150 g / m ² .

If hot melt adhesives are used in the process according to the invention, they are preferably applied in the molten state to the surface of the thinner foam boards to be bonded. The implementation of the melting of a hotmelt adhesive is known in the art.

In one embodiment of the present invention, the adhesive, such as a molten-state hot melt adhesive, is applied to at least one surface of at least one thinner foam sheet, the application of the adhesive being uniform in one direction of the respective sheet surface.

This embodiment is also referred to as an application (of the adhesive) under bias.

As already mentioned above, in addition to the adhesive, it is also possible to apply further substances with different use properties to the surface to be bonded of the corresponding thinner foam boards. Suitable further substances may be, for example, flame retardants, graphite, absorbers of electromagnetic radiation and / or binders and, if appropriate, solvents. Flame retardants, graphite, absorbers of electromagnetic radiation, binders and solvents as such are known to the person skilled in the art. The aforementioned optional components may be used alone or in any combination with the adhesives.

In one embodiment of the method according to the invention, the adhesive is part of a mixture which additionally contains at least one flame retardant and / or graphite.

Flame retardants as such are known in the art. Suitable flame retardants are, for example, in Jürgen Troitzsch "Plastics Flammability Handbook" (3rd ed., Hanser Verlag) described. Preferred flame retardants in the context of the present invention are selected from a phosphate, a phosphite, a phosphonate, a polyphosphonate, melamine, a metal oxide hydrate, in particular an aluminum oxide hydrate, or a halogenated organic compound.

Preferred phosphates and phosphonates are selected from DMMP (dimethymethyl phosphonate), DMPP (dimethyl propyl phosphonate), TCEP (tris (chloroethyl) phosphate), TCPP (tris (chloropropyl) phosphate), TDCPP (tris (dichloroisopropyl) phosphate), TPP (triphenyl phosphate), TEHP (Tris (2-ethylhexyl) phosphate), TKP (tricresyl phosphate) or TCEP (trichloropropyl phosphate).

A particularly preferred flame retardant is dimethylpropylphosphonate (DMPP), which is commercially available, for example, under the name Levagard DMPP from Lanxess.

Examples of combinations of flame retardants or graphite with adhesives according to the invention are listed below.

If aqueous adhesives are used, they preferably contain a flameproofing agent to be added as aqueous formulation; a commercially available example of this is Exolit RP 614 from Clariant SE.

Non-water-soluble flame retardants or graphite are preferably admixed as a fine powder with the aid of pigment dispersants and surfactants, examples being melamine, melamine cyanurate, melamine (poly) phosphate, melamine phenylphosphonate, expandable graphite, aluminum hydroxide. Filled dispersions find application, some of the fillers can be replaced by a solid, non-soluble flame retardant.

As polyurethane dispersions preferred. Secondary dispersions are, it is possible to give flame retardants during the production in the organic phase, are particularly suitable organic soluble types such as DMPP, triphenyl phosphate, even peroxides such as dicumyl peroxide can be used. This procedure allows a particularly good distribution of flame retardants in the polymer particles. Also, halogenated polyols can be used as structural components in aqueous as well as reactive polyurethane adhesives.

Alternatively, the flame retardants are liquid and soluble or water-dispersible in water; dimethylpropyl phosphonate (DMPP) is particularly suitable.

For non-aqueous adhesives, organic soluble flame retardants such as DMPP are preferred, other suitable substances are in the WO 2003/051954 especially for polyurethane adhesives described.

Non-water-soluble flame retardant or graphite are preferably track levels as a fine powder, examples are expandable graphite, commercially available as Melapur MC ^® and Melapur MP ^® from BASF. Powdered flame retardants can also be surface-modified, so that a good distribution is possible.

• i) die Gesamtmenge an Flammschutzmittel ≥ 4 Gew.-% (bezogen auf die Gesamtmenge an Klebstoff) beträgt, oder
• ii) die Gesamtmenge an Flammschutzmittel ≥ 2,5 Gew.-% beträgt, sofern das Flammschutzmittel als Gemisch mit mindestens 2,5 Gew.-% Graphit eingesetzt wird (Mengenangaben jeweils bezogen auf die Gesamtmenge an Klebstoff).

In one embodiment of the method according to the invention, a mixture comprising at least one adhesive and at least one flame retardant is applied to at least one surface of at least one thinner foam sheet, wherein in the mixture

• i) the total amount of flame retardant ≥ 4 wt .-% (based on the total amount of adhesive) is, or
• ii) the total amount of flame retardant ≥ 2.5 wt .-%, if the flame retardant is used as a mixture with at least 2.5 wt .-% graphite (quantities in each case based on the total amount of adhesive).

In the mixture containing at least one adhesive and at least one flame retardant (according to the first variant of the present embodiment), the total amount of flame retardant ≥ 4 wt .-% (based on the total amount of adhesive), preferably, the total amount of flame retardant 4.5 bis 15 wt .-% (based on the total amount of adhesive), in particular, the total amount of flame retardant 5 to 10 wt .-% (based on the total amount of adhesive).

In this embodiment of the present invention, the total amount of flame retardant (second variant) can also be slightly less than ≥ 4 wt .-% (based on the total amount of adhesive), if the flame retardant is used as a mixture with graphite, preferably with expandable graphite. According to the second variant, the total amount of flame retardant ≥ 2.5 wt .-%, if the flame retardant is used as a mixture with at least 2.5 wt .-% graphite (quantities in each case based on the total amount of adhesive). According to the second variant, the total amount of flame retardant is preferably ≥ 3.5% by weight (based on the total amount of adhesive), more preferably the total amount of flame retardant is 4.5 to 15% by weight (based on the total amount of adhesive In particular, the total amount of flame retardant is 5 to 10% by weight (based on the total amount of adhesive). The total amount of graphite, preferably of expandable graphite; is preferably ≥ 4 wt .-% (based on the total amount of adhesive), in particular, the total amount of graphite is 5 to 10 wt .-% (based on the total amount of adhesive).

In one embodiment of the method according to the invention, the adhesive is part of a mixture which comprises at least one absorber of electromagnetic radiation ("absorber"). Suitable absorbers are for example in WO 2009/071499 on pages 9 to 11. In the context of the present invention, an absorber of electromagnetic radiation is generally used when, in addition to bonding, preferably simultaneously or subsequently, a thermal welding step is carried out. If appropriate, at least one absorber of electromagnetic radiation can additionally be applied to at least one thinner foam board without a thermal welding step being carried out. Preferably, in the context of the present invention, the absorber of electromagnetic radiation is selected as a function of the electromagnetic radiation used for thermal welding. For example, when thermal welding is performed using microwave rays, it is preferable to select an electromagnetic radiation absorber having a good absorption ability in the microwave wavelength region.

Suitable absorbers are, for example, organic IR absorbers, organic microwave absorbers, inorganic IR absorbers or inorganic microwave absorbers.

For the purposes of this application, an IR absorber is understood as meaning a compound which has an absorption of ≥ 90% when applied in a layer thickness of 50 μm, when irradiated with at least one wavelength from a wavelength range from 700 nm to 1. Preferably, the wavelength range of> 700 nm to 2000 nm, and the wavelengths 9.6 microns and 10.6 microns.

In the context of this application, microwave absorber is to be understood as meaning a compound which absorbs microwaves of the wavelength range of> 1 mm to 1 m. Particularly preferred are the technically relevant frequencies of 2.45 GHz, 433-444 MHz and 902-928 MHz.

Preferably, the absorber of electromagnetic radiation is an infrared (IR) absorber and / or microwave absorber, in particular graphite or carbon black. Furthermore, it is preferred that the electromagnetic radiation are IR rays and / or microwave rays.

The performance of the thermal welding as such is known to the person skilled in the art. The person skilled in the art also knows the equipment required for generating the suitable electromagnetic radiation. For example, a coated plate in the second to minute range can be irradiated in a microwave oven or with an IR radiator. According to the invention, thermal welding is carried out only if at least one thinner foam plate has been previously applied with at least one absorber of electromagnetic radiation. Preferably, the thermal welding is carried out after the joining of the thinner foam boards to the surfaces to be bonded or following a compression of the assembled thinner foam boards.

If in the context of the present invention, a thinner foam board, to which preferably at least one adhesive and optionally further components such as flame retardants have been applied, is exposed to electromagnetic radiation without an absorber of electromagnetic radiation being applied to the corresponding thinner foam board such an operation in the context of the present invention is not referred to as thermal welding, but as activation of said thinner foam sheet. Typically, activation will occur after the adhesive has been applied to at least one adherend surface of the thin foam sheets, preferably following a drying step of the thin foam sheets provided with the above mixture. Optionally, the activation step can also be carried out after joining the thinner foam sheets to the surfaces to be bonded or following compression of the assembled thinner foam sheets.

Furthermore, in the mixture containing at least one adhesive and at least one flame retardant and / or graphite and binder may be present, preferably if it is additionally contained in the mixture at least one absorber of electromagnetic radiation.

Suitable binders in the context of the present invention are selected from polyacrylates and copolymers thereof, polystyrene and copolymers thereof, ethylene-acrylate copolymers, ethylene-vinyl acetate copolymers, polyurethanes and polyurethane-acrylate hybrids. Preferred copolymers of polystyrene are styrene-butadiene copolymers.

Preferred binders are selected from aqueous dispersions or solutions of polyacrylates and copolymers thereof, polystyrene and copolymers thereof, ethylene-acrylate copolymers, ethylene-vinyl acetate copolymers, polyurethanes and polyurethane-acrylate hybrids. Preferred copolymers of polystyrene are styrene-butadiene copolymers.

Particularly preferred binders are dispersions with a high proportion of polystyrene or copolymer thereof, in particular with a high proportion of polystyrene. These dispersions are preferably used when in the process according to the invention the thinner thermoplastic foam boards (starting boards) also contain polystyrene or copolymers thereof, because then the properties of the at least two-ply thermoplastic foam boards (composite panels) differ even less from the starting boards due to the use of said binder.

In a preferred embodiment of the present invention, the adhesive is applied to at least one surface of at least one thinner foam sheet, the surface being free of skin foam. For completeness, it is pointed out that when using an extrusion foam, the corresponding surface is also referred to as extrusion skin-free instead of foam-skin-free.

In a further preferred embodiment of the present invention, the method is carried out so that each surface to be bonded of the thinner foam sheets is free of foaming skin.

In another embodiment, it is preferred that the adhesive is applied to only one adherend surface of the thinner foam sheets per adhesive pair to be bonded. In one embodiment of the present invention, if a thermal welding step is additionally performed, at least one thinner foam sheet is additionally added an absorber of electromagnetic radiation has been applied, heated by the irradiation with electromagnetic radiation to temperatures above the glass transition temperature of the foam sheet.

Furthermore, it is preferred that in the method according to the invention, a compression of the thinner foam panels joined together on the surfaces to be bonded is carried out. The compression is generally carried out in the minute range and / or at a compression pressure of 0.01 to 0.5 bar. The process according to the invention is preferably carried out with a pressure of from 0.01 to 0.1 bar and / or a pressing time of ≦ 1 second.

Furthermore, in the process according to the invention, a drying step is carried out after the hotmelt adhesive, optionally in the form of a mixture with further components such as flame retardants, has been applied to the surface of the thinner thermoplastic foam boards. Drying normally takes place for a period of ten minutes to two hours and / or at a temperature in the range of 50 to 100 ° C. The drying step is preferably not required in the process according to the invention if a hot melt adhesive is used as adhesive.

• a) Bereitstellen von mindestens zwei dünneren Schaumstoffplatten, wobei jede zu verklebende Oberfläche der dünneren Schaumstoffplatten schäumhautfrei ist,
• b) strukturiertes Aufbringen von mindestens einem Klebstoff auf (pro zu verklebendem Plattenpaar) mindestens eine zu verklebende Oberfläche der dünneren Schaumstoffplatten,
• c) gegebenenfalls Trocknen der dünneren Schaumstoffplatten, die in Schritt b) erhalten wurden,
• d) gegebenenfalls Aktivieren der getrockneten dünneren Schaumstoffplatten mit elektromagnetischer Strahlung,
• e) Zusammenfügen der dünneren Schaumstoffplatten an den zu verklebenden Oberflächen,
• f) Verpressen der zusammengefügten dünneren Schaumstoffplatten und gegebenenfalls anschließendes Aushärten unter Erhalt einer zumindest zweilagigen Schaumstoffplatte.

In a further preferred embodiment in the present invention, the method comprises the following steps:

• a) providing at least two thinner foam sheets, each surface of the thinner foam sheets to be bonded being free of foaming skin,
• b) structured application of at least one adhesive on (per pair of plates to be bonded) at least one surface to be bonded of the thinner foam plates,
• c) optionally drying the thinner foam boards obtained in step b),
• d) optionally activating the dried thinner foam sheets with electromagnetic radiation,
• e) joining the thinner foam boards to the surfaces to be bonded,
• f) pressing the assembled thinner foam sheets and optionally subsequent curing to obtain an at least two-layer foam sheet.

The curing in the above-described step f) is preferably carried out when a polyurethane adhesive is used as the adhesive. If a hot-melt adhesive is used in this process (in step b)), it is no longer necessary to carry out the drying step c). Furthermore, the melt adhesive is preferably melted when using hot melt adhesives prior to step b).

Another object of the present invention are the foam sheets as such, which are at least two layers and can be produced by the method described above.

The invention will be clarified below with reference to the examples.

Styrodur is a commercial product of BASF SE in the form of an extruded polystyrene foam (XPS). The plates used in the examples all have a thickness of 45 mm.

In the embodiments 1 to 5, the respective adhesives are grid-shaped (ie a lower form of lattice-shaped) with the structural unit crosses on (per pair of plates) each applied only one surface to be bonded by a thinner foam plate, each provided with about 75% of the plate surface with adhesive become. On the other hand, the foaming skin on each pair of plates is previously removed on both surfaces to be bonded.

Examples according to the invention

example 1

An aqueous polyurethane dispersion (Luphen D 259 U, BASF SE) is admixed with 5% by weight of an aqueous polyisocyanate hardener (Basonat F 200 WD, BASF SE). On a Styrodurplatte (100 × 100 mm ² ) without Schäumhaut so much aqueous adhesive formulation is applied in a grid with a brush, that after drying for 30 min at 75 ° C 80-120 g / m ² dry adhesive. The grid consists of crosswise applied strips of glue, which are about 10 mm wide and repeat every 10 mm. The adhesive layer is heated for 5 seconds under an IR emitter (IRE 380, OPTRON Messtechnik GmbH) and a second analog Styrodur plate without foaming skin is applied and loaded with 2 kg for 60 seconds. The composite is cured for 5 days at room temperature. The adhesive tensile strength (according to DIN EN 1607 ) is 0.20 N / mm ² . The sample passes the fire test B2 (after DIN 4102 ).

Example 2

An aqueous polyurethane dispersion (Luphen 3615, BASF SE) is admixed with 5% by weight of an aqueous polyisocyanate hardener (Basonat F 200 WD, BASF SE). On two Styrodur plates (100 × 100 mm ² ) without foaming skin, so much aqueous adhesive formulation is applied with a brush in a grid shape that after drying for 30 min at 75 ° C 40-60 g / m ² dry adhesive on each plate. The grid consists of crosswise applied strips of glue, which are about 10 mm wide and repeat every 10 mm. The adhesive layers are heated under an IR emitter (IRE 380, OPTRON Messtechnik GmbH) for 5 seconds and (layer by layer) combined and loaded with 10 kg for 90 seconds. The composite is cured for 5 days at room temperature. The adhesive tensile strength (according to DIN EN 1607 ) is 0.30 N / mm ² . The sample passes the fire test B2 (after DIN 4102 ).

Example 3

On a 100 mm × 100 mm Styrodurplatte without foaming skin 2.5 g of an aqueous assembly adhesive (formulated according to the example of EP 1 268 698 ) with a toothed spatula applied in a grid pattern. The grid consists of crosswise applied strips of glue, which are about 10 mm wide and repeat every 10 mm. A second analog Styrodurplatte without foaming skin is placed and loaded with 10 kg for 90 seconds. The composite is cured for 5 days at room temperature. The adhesive tensile strength (average of three patterns) analog DIN EN 1607 is 0.22 N / mm ² . The sample passes the fire test B2 (after DIN 4102 ).

Example 4

On a 100 mm × 100 mm Styrodur plate without foaming skin, an aqueous polymer dispersion based on styrene-acrylate copolymers (Acronal S 790, BASF SE) is applied with a brush in the form of a grid (about 1.5 g). The grid consists of crosswise applied strips of glue, which are about 10 mm wide and repeat every 10 mm. A second analog Styrodurplatte without foaming skin is placed and loaded with 10 kg for 90 seconds. The composite is dried for 5 days at room temperature. The adhesive tensile strength (according to DIN EN 1607 ) is 0.22 N / mm ² . The sample passes the fire test B2 (after DIN 4102 ).

Example 5

On a 100 mm × 100 mm Styrodurplatte without foaming skin 2 g of an insulating adhesive (Kleiberit Apripur 509) are applied with a razor-shaped grid. The grid consists of crosswise applied strips of glue, which are about 10 mm wide and repeat every 10 mm. 20 g / m ^{2 of} water are sprayed on and a second analogous Styrodur plate without foaming skin is applied and loaded with 10 kg for 90 seconds. The composite is then cured for 5 days at room temperature. The adhesive tensile strength (average of three patterns) analog DIN EN 1607 is 0.35 N / mm ² . The sample passes the fire test B2 (after DIN 4102 ).

Comparative Examples

Comparative Example 1

An aqueous polyurethane dispersion (Luphen D 259 U, BASF SE) is admixed with 5% by weight of an aqueous polyisocyanate hardener (Basonat F 200 WD, BASF SE). On a Styrodurplatte (100 × 100 mm ² ) without Schäumhaut so much aqueous adhesive formulation is applied with a brush over the same surface, that after drying for 30 min at 75 ° C 80-120 g / m ² dry adhesive. The adhesive layer is heated for 5 seconds under an IR emitter (IRE 380, OPTRON Messtechnik GmbH) and a second analog Styrodur plate without foaming skin is applied and loaded with 2 kg for 60 seconds. The composite is cured for 5 days at room temperature. The adhesive tensile strength (according to DIN EN 1607 ) is 0.22 N / mm ² . The sample does not pass the fire test B2 (after DIN 4102 ).

Comparative Example 2

An aqueous polyurethane dispersion (Luphen 3615, BASF SE) is admixed with 5% by weight of an aqueous polyisocyanate hardener (Basonat F 200 WD, BASF SE). On two Styrodur plates (100 × 100 mm ² ) without foaming skin, so much aqueous adhesive formulation is evenly applied with a brush so that after drying for 30 minutes at 75 ° C. 40-60 g / m ^{2 of} dry adhesive are present on each plate. The adhesive layers are heated under an IR emitter (IRE 380, OPTRON Messtechnik GmbH) for 5 seconds and (layer by layer) combined and loaded with 10 kg for 90 seconds. The composite is cured for 5 days at room temperature. The adhesive tensile strength (according to DIN EN 1607 ) is 0.34 N / mm ² . The sample does not pass the fire test B2 (after DIN 4102 ).

Comparative Example 3

On a 100 mm × 100 mm Styrodurplatte without foaming skin 2.5 g of an aqueous assembly adhesive (formulated according to the example of EP 1 268 698 ) applied evenly with a wooden spatula. A second analog Styrodurplatte without foaming skin is placed and loaded with 10 kg for 90 seconds. The composite is cured for 5 days at room temperature. The adhesive tensile strength (average of three patterns) analog DIN EN 1607 is 0.24 N / mm ² . The sample does not pass the fire test B2 (after DIN 4102 ).

Comparative Example 4

An aqueous polymer dispersion (Acronal S 790, BASF SE) is uniformly applied with a brush to a 100 mm × 100 mm Styrodur plate without foam skin (about 1.5 g). A second analog Styrodurplatte without foaming skin is placed and loaded with 10 kg for 90 seconds. The composite is dried for 5 days at room temperature. The adhesive tensile strength (according to DIN EN 1607 ) is 0.24 N / mm ² . The sample does not pass the fire test B2 (after DIN 4102 ).

Comparative Example 5

On a 100 mm × 100 mm Styrodur plate without foam skin, apply 1.7 g of an insulating adhesive (Kleiberit Apripur 509) evenly with a wooden spatula. 20 g / m ^{2 of} water are sprayed on and a second analogous Styrodur plate without foaming skin is applied and loaded with 10 kg for 90 seconds. The network will be 5 days afterwards cured at room temperature. The adhesive tensile strength (average of three patterns) analog DIN EN 1607 is 0.4 N / mm ² . The sample does not pass the fire test B2 (after DIN 4102 ).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1318164 A [0002, 0002]
• EP 1213119A [0003]
• EP 1566400 A [0004, 0004]
• DE 101063341 A [0005, 0005]
• EP 1471125 A [0006, 0006]
• WO 2012/016991 [0007, 0007]
• WO 2009/047487 [0008, 0024]
• EP 1566490A [0024]
• EP 1879974 A [0033]
• WO 2003/051954 [0067]
• WO 2009/071499 [0072]
• EP 1268698 [0096, 0101]

Cited non-patent literature

• DIN 4102 [0009]
• DIN EN ISO 11925-2: 2011-02 [0009]
• DIN 4102 [0013]
• DIN EN ISO 11925-2: 2011-02 [0013]
• Jürgen Troitzsch "Plastics Flammability Handbook" (3rd ed., Hanser Verlag) [0059]
• DIN EN 1607 [0094]
• DIN 4102 [0094]
• DIN EN 1607 [0095]
• DIN 4102 [0095]
• DIN EN 1607 [0096]
• DIN 4102 [0096]
• DIN EN 1607 [0097]
• DIN 4102 [0097]
• DIN EN 1607 [0098]
• DIN 4102 [0098]
• DIN EN 1607 [0099]
• DIN 4102 [0099]
• DIN EN 1607 [0100]
• DIN 4102 [0100]
• DIN EN 1607 [0101]
• DIN 4102 [0101]
• DIN EN 1607 [0102]
• DIN 4102 [0102]
• DIN EN 1607 [0103]
• DIN 4102 [0103]

Claims (18)

A method of producing at least two-ply foam sheets by adhering at least two thinner foam sheets to the at least two-ply foam sheet, characterized in that at least one adhesive is patterned on at least one surface of at least one thinner foam sheet, on the surface of the thinner foam sheet on which the adhesive is applied structured, 20 to 90% of the respective plate surface are provided with adhesive. A method according to claim 1, characterized in that 40 to 80%, in particular 50 to 75%, of the respective plate surface are provided with adhesive on the surface of the thinner foam board on which the adhesive is applied structured. A method according to claim 1 or 2, characterized in that the adhesive is punctiform, linear or lattice-shaped, preferably grid-shaped, is applied to at least one surface of at least one thinner foam sheet. A method according to any one of claims 1 to 3, characterized in that the thinner foam sheet is a particle foam or an extrusion foam, preferably an extrusion foam of polystyrene or of a copolymer made of styrene. Method according to one of claims 1 to 4, characterized in that the adhesive is a dispersion adhesive. A method according to claim 5, characterized in that the dispersion adhesive is a contact adhesive or laminating adhesive based on a dispersion of polyacrylate, styrene-acrylate copolymers or polyurethane. Method according to one of claims 1 to 4, characterized in that the adhesive is a hot melt adhesive. A method according to claim 7, characterized in that the hot melt adhesive is a moisture-curing polyurethane hot melt adhesive. A method according to claim 7, characterized in that the hot melt adhesive comprises at least one polymer (P1) selected from the group of polyolefins, polyesters, polyamides, polyacrylates, styrene-isoprene copolymers, styrene-butadiene copolymers, ethylene-vinyl acetate -Copolymers or polyvinyl acetate (PVA). A method according to any one of claims 7 to 9, characterized in that the hot melt adhesive is applied in molten state on at least one surface of at least one thinner foam sheet, wherein the application of the hot melt adhesive takes place uniformly in a direction of the respective plate surface. A method according to any one of claims 1 to 10, characterized in that the adhesive is applied to at least one surface of at least one thinner foam sheet, wherein the surface is free from foaming skin. A method according to any one of claims 1 to 11, characterized in that each surface to be bonded of the thinner foam sheet is free of foam and / or that is applied per adhesive pair to be bonded to only one surface to be bonded to the thinner foam sheets. Method according to one of claims 1 to 12, characterized in that the adhesive is part of a mixture which additionally contains at least one flame retardant and / or graphite. A method according to claim 13, characterized in that the flame retardant is selected from a phosphate, a phosphite, a phosphonate, a polyphosphate, melamine, a metal oxide hydrate or a halogenated organic compound. A method according to any one of claims 1 to 14, characterized in that the adhesive in amounts of 20 to 400 g / m ² (based on the adherend surface of a plate per plate pair) is applied. Method according to one of claims 1 to 15, characterized in that the width of a structural unit of the structured applied adhesive 5 to 50 mm and / or the distance between the individual structural units of the structured applied adhesive 5 to 50 mm. A method according to any one of claims 1 to 16, comprising the following steps: a) providing at least two thinner foam sheets, each surface of the thinner foam sheets to be bonded being free of foam, b) applying at least one adhesive to at least one (per pair of sheets to be bonded) at least one c) adhering surface of the thinner foam sheets, c) optionally drying the thinner foam sheets obtained in step b), d) optionally activating the dried thinner foam sheets with electromagnetic radiation, e) assembling the thinner foam sheets to the surfaces to be bonded, f) compressing the assembled thinner sheets of foam and optionally subsequently curing to obtain an at least two-ply foam sheet. Foam board, which is at least two layers, can be produced by a process according to one of claims 1 to 17.