WO2016102291A1

WO2016102291A1 - Method for producing multi-layered foam plates having structured recesses by means of thermal welding

Info

Publication number: WO2016102291A1
Application number: PCT/EP2015/080178
Authority: WO
Inventors: Dietrich Scherzer; Carsten Sandner; Tim Diehlmann; Franz-Josef Dietzen
Original assignee: Basf Se
Priority date: 2014-12-22
Filing date: 2015-12-17
Publication date: 2016-06-30
Also published as: EP3237175A1

Abstract

The invention relates to a method for producing at least two-layered thermoplastic foam plates by means of thermal welding of at least two thinner thermoplastic foam plates, comprising the steps a), b), and c). In step a), structured recesses are introduced into at least one contact surface of at least one of the thinner thermoplastic foam plates. In step b), at least one thinner thermoplastic foam plate is heated on the contact surface thereof, which has the structured recesses. In step c), the contact surfaces of the at least two thinner thermoplastic foam plates are brought into contact, forming a weld seal. According to the invention, step c) is carried out no later than 2 seconds after completing step b).

Description

Process for producing multilayer foam sheets with structured depressions by thermal welding

description

The present invention relates to a process for the production of at least two-ply thermoplastic foam boards by thermal welding of at least two thinner thermoplastic foam boards comprising steps a), b), c). In step a), structured depressions are introduced into at least one contact surface of at least one of the thinner thermoplastic foam sheets. In step b), at least one thinner thermoplastic foam sheet is heated at its contact surface having the structured recesses. In step c), the contact surfaces of the at least two thinner thermoplastic foam sheets are brought into contact to form a weld. In this case, step c) is carried out not later than 2 seconds after the end of step b).

Furthermore, the present invention relates to the thermoplastic foam sheets as such, which are at least two-ply. As such, the number of layers of the thermoplastic foam sheet results from the number of thinner thermoplastic foam sheets which are thermally welded together. For example, when three thinner thermoplastic foam sheets are thermally welded together, a three-layered thermoplastic foam sheet is obtained as such, thus, in the case of four thinner thermoplastic foam sheets, a four-layered thermoplastic foam sheet as such results.

EP-A-1 318 64 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 process according to EP-A 1318 164, the foaming skins can be peeled on the main surfaces of the plates to be joined together before they are wetted with the solvent. Thermal welding is not the subject of EP-A 1 318 164. EP-A 1 213 119 discloses a method for connecting at least two thermoplastic resin foam starting sheets to a new sheet, wherein the starting sheets are extrusion skinless at the contact surfaces and the source sheets are joined 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. A method using thermal welding is not disclosed. Extruded plastic foam sheets of great thickness are disclosed in DE-A 101 063 341. With the method described therein for connecting at least two plastic foam starting plates to a new plate, plates with a minimum thickness of 70 mm can be produced. 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 bonding. As polystyrene foam boards are particularly suitable XPS boards. In DE-A 101 063 341, however, no information is given as to how the welding of the starting plates can be performed concretely instead of gluing, nor is it disclosed therein that the starting plates can have structured depressions. Accordingly, it is also not mentioned that a weld is formed at points with structured depressions, which has a reduced strength compared to the locations without structured depressions.

DE-A 44 21 016 discloses a process for the production of C0 ₂ foamed plastic plates of large thickness, in particular of polystyrene and / or polyethylene, wherein a duplication of the corresponding output plates is carried out by thermal welding. The thermal welding can be carried out with the aid of a heating sword, whereby the surfaces of the plastic foam sheets used are melted. The heating element can be brought to the necessary welding temperature either electrically or with a heating medium flowing through, which, depending on the plastic foam, is between 100 and 150 ° C. Also in DE-A 101 063 341 no information is included that the output plates may have structured depressions. EP 2 687 353 A1 relates to a process for the production of at least two-ply thermoplastic foam boards by thermal welding of at least two thinner thermoplastic foam boards. It is At least one surface of at least one thinner thermoplastic foam plate provided with structured recesses and at the points where the surface of the thinner thermoplastic foam sheet having the structured recesses, is formed by the thermal welding no weld. A time difference between the completion of the heating of the thermoplastic foam sheets and the bringing into contact of the thermoplastic foam sheets to be welded is not mentioned.

Thermal insulation materials of XPS composite materials, which are three-layered, are described in WO 2012/016991. The trilayer 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. The formed between the individual XPS plates weld may have portions of different intensity, which means that the corresponding weld is stronger in some places, but weaker in other places. WO 2012/016991 contains no information on the time difference between the termination of the heating step and the bringing into contact of the XPS plates to be welded. EP-A-2 687 354 relates to thermoplastic foam boards having a weld thickness of 200 to 300 μm and to a method for the production thereof by thermal welding of at least two thinner thermoplastic foam boards. The resulting thermoplastic SchaumstoffpMten are thus at least two layers. Structured depressions can also be incorporated in the thinner thermoplastic foam boards. In EP-A 2 687 354, however, nowhere is it described that the corresponding contact surfaces of the thinner thermoplastic foam boards are brought into contact with each other no later than two seconds after completion of the previous heating step.

EP-A 2 669 072 relates to a process for the production of at least two-ply thermoplastic foam sheets by thermal welding of at least two thinner thermoplastic foam sheets, at least one absorber of electromagnetic radiation being applied to at least one surface of at least one thinner thermoplastic foam sheet. However, EP-A 2 669 072 does not disclose anywhere that the corresponding thinner thermoplastic foam sheets may have structured recesses.

EP-A 2 153 982 relates to a sheet-like structural element as a section of a foam block. The foam block itself comprises a plurality of welded foam bodies and is therefore at least two-ply. The foam body may also contain thermoplastics. The foam bodies may be structured with grooves, grooves or grooves which may be applied both before heating and during or immediately after heating the foam body. The contact surfaces are also brought into contact with the formation of a weld. Nowhere, however, is it mentioned that the contacting can be carried out not later than two seconds after completion of the heating. During thermal welding, the foam sheet is first melted locally, since the resulting melt serves to form the weld seam. As the amount of molten material increases, the thickness of the weld increases and thus its strength increases. But this melting process in connection with the welding is also accompanied by a loss of thickness of the materials to be welded. It is therefore an objective in welding, this weld as thin as possible and thus to minimize the loss of thickness of the materials to be welded. On the other hand, the strength of the weld should also be as homogeneous as possible and have a certain minimum tensile strength at each point.

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

The object is achieved by methods for producing at least two-layer thermoplastic foam sheets by thermal welding of at least two thinner thermoplastic foam sheets to the at least two-layer thermoplastic foam sheet comprising steps a), b), c): a) introducing structured depressions into at least one Contact surface of at least one of the thinner thermoplastic foam sheets, b) heating at least one thinner thermoplastic foam sheet at its contact surface having the structured depressions, c) contacting the contact surfaces of the at least two thinner thermoplastic foam sheets to form a weld, wherein step c) is performed not later than 2 seconds after the completion of step b).

The at least two-ply thermoplastic foam boards produced by the process according to the invention are characterized in that they have an increased minimum tensile strength of the weld seam, preferably of at least 0.1 N, with the same foam loss compared to two-ply thermoplastic foam boards obtained by welding thermoplastic foam boards without structured depressions / mm ^{2 is} achieved. In addition, the homogeneity of the weld strength is significantly increased. In addition, the two-ply thermoplastic foam sheets according to the invention simultaneously have improved flame retardancy.

A particularly stable cohesion of the individual thinner thermoplastic foam sheets is achieved when the thinner thermoplastic foam sheets are additionally provided with an absorber of electromagnetic radiation, with electromagnetic radiation of suitable wavelength (for example, IR radiation or microwave radiation) are irradiated and / or on Temperatures are heated above the glass transition temperature of the thermoplastic used. Preferably, the individual thinner thermoplastic foam sheets are then additionally pressed together. The at least two-layer thermoplastic foam boards produced by the process according to the invention, in particular those in which the surface of the foam boards are heated to temperatures above the glass transition temperature, have as a further advantageous property a high water vapor permeability and / or strength of the thermally welded foam sheets.

If the inventive method is carried out using an absorber of electromagnetic radiation, wherein the absorber is applied to the corresponding surfaces of the thinner thermoplastic foam sheets which are thermally welded together, a further advantage is the fact that the radiation transmissibility of at least two-ply thermoplastic Foam boards as such is reduced and / or the thermal conductivity behavior can be improved. The thermal conductivity can be reduced by up to 10% compared to conventional plates, where no absorber of electromagnetic radiation is used. A reduction in thermal conductivity means a (thermal) insulation effect. Hereinafter, the invention at least two-layer thermoplastic foam sheets as such and the inventive manufacturing method of these foam sheets are defined by thermal welding closer.

The first subject of the present invention is a process for producing at least two-ply thermoplastic foam sheets by thermally welding at least two thinner thermoplastic foam sheets to the at least two-ply thermoplastic foam sheet comprising steps a), b), c).

The thermoplastic foam sheet produced by the process according to the invention and the thermoplastic foam sheet according to the invention as such is at least two layers, so it may 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 thermoplastic foam sheet as such results from the number of thinner thermoplastic foam sheets, which are thermally welded together. The thin thermoplastic foam boards are also called output boards. In the case of a two-ply thermoplastic foam board as such, therefore, two thinner thermoplastic foam boards are thermally welded together. In a three- or four-layer thermoplastic foam sheets as such, three or four thinner thermoplastic foam sheets are thus thermally welded together. If even higher-layered thermoplastic foam sheets are to be produced as such, for example a ten-ply thermoplastic foam sheet, the number of layers corresponding number of thinner thermoplastic foam sheets, for example, ten thinner thermoplastic foam sheets, must be thermally welded together. Preferably, the thermoplastic foam sheet according to the invention is two-ply, three-ply or four-ply.

With regard to their chemical composition, the thinner thermoplastic foam boards used for thermal welding correspond to the at least two-layered thermoplastic foam boards produced as part of the process according to the invention (without consideration of the components optionally applied to the surfaces during the welding process, such as absorbers of electromagnetic radiation or binder or without Consideration of the chemical changes / reactions occurring as a result of the formation of the weld on the corresponding surfaces). The respective thinner thermoplastic foam sheets to be thermally welded together preferably have the same dimensions and / or the same chemical composition. If necessary, but also thermoplastic foam sheets with different dimensions and / or different chemical composition are thermally welded together. For example, when three thinner thermoplastic foam sheets are heat sealed together, all of which have the same sizing and are (for example) an extruded polystyrene foam (XPS foam), a three-ply thermoplastic extruded polystyrene foam (XPS) is obtained.

The thinner thermoplastic foam boards used for thermal welding as such are known in principle to the person skilled in the art. Suitable thermoplastic foam boards are disclosed for example in the form of blends in WO 2009/047487. For example, plates of amorphous, crystalline or semi-crystalline thermoplastic foams can be used. Preferably, the thinner thermoplastic foam sheets are a particle foam or an extrusion foam. Furthermore, it is preferred that the thinner thermoplastic foam sheets have a density <200 g / l, preferably a density of <100 g / l. Preferred particles are polystyrene foams ^®, Neopor ^®, E-por ^®, which are commercially available from BASF SE. More preferably, the thinner thermoplastic foam sheets are an extrusion foam. The extrusion foam is preferably a polystyrene or styrene-made copolymer. Preference is also given to extrusion foams of PET (polyethylene terephthalate), as are produced, for example, by the companies Diab and Armacell. Optionally, mixtures of such polymers can be used. The extruded foam is particularly preferably 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 copolymer made of styrene (also referred to as styrene copolymers), this means that at least one further monomer is required in addition to the monomer styrene 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 copolymer made of styrene as a comonomer to styrene has a monomer selected from α-methylstyrene, ring-halogenated styrenes, ring-alkylated styrenes, acrylonitrile, acrylic 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).

The dimensioning of the thermally to be welded together thinner thermoplastic foam boards 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 thermoplastic foam sheets have a thickness of 10 to 150 mm. The thickness of the at least two-layer thermoplastic foam boards produced in the process according to the invention thus results from the total thickness of the thinner thermoplastic foam boards used (starting boards).

Due to the thermal welding, the respective surfaces of the output plates to be welded together are at least slightly fused or melted (melting step), which depending on the amount of heat supplied can lead to a certain reduction of the thickness of the respective output plate (foam loss). They also other versions for thermal welding.

In the context of this invention, the term "foam loss" refers to the thickness loss of the foam sheet to be welded, measured in loss of length of the side of each foam plate in mm perpendicular to the weld or the contact surface with the other foam plate, with the foam plate to be welded, in the welding process which is considered welded.

The term "contact surface" of a thinner thermoplastic foam sheet is understood to mean the surface of this sheet which, as part of the welding, is brought into contact with the other thinner thermoplastic foam sheet to be welded, and via which the compound of the two thinner thermoplastic foam sheets is produced. Alternatively, the contact surface may be referred to as a "surface to be welded" prior to welding.

In step a), structured depressions are introduced into at least one contact surface of at least one of the thinner thermoplastic foam sheets.

According to the invention, at least one surface of at least one thinner thermoplastic foam plate is provided with structured depressions, wherein at least one of these surfaces, which is provided with structured depressions, is also thermally welded and thus constitutes a contact surface. At a Thus, in the case of two three starting plates to be welded, it is possible for a three-layer thermoplastic foam plate to have a surface with structured recesses or only one starting plate (the central one) is structured on both surfaces, but the two other starting plates are unstructured. Preferably, one contact surface of a thinner thermoplastic foam sheet is provided with structured depressions per pair of plates to be welded.

The patterned depressions may be formed on the corresponding surface of a thinner thermoplastic foam sheet, which is also typically a contact surface, by any methods known to those skilled in the art. The structured depressions are preferably produced by planing or milling, in particular by milling, the surface of the thinner thermoplastic foam boards. The structured depressions can be produced on a surface (the starting plate) which has a foaming skin or which is free of foaming skin. The planing or milling to produce a surface with structured depressions differs from the planing or milling described for step d) to produce a foaming skin-free surface in particular in that in the case of creating a surface with structured depressions planing or milling at selected locations / subareas the appropriate surface is selectively carried out to produce the desired structural unit / pattern. Alternatively, the patterned depressions on the corresponding surface can also be generated in situ during thermal welding, for example using devices having nubs or grooves.

The spacings between the individual structural units of a structured depression on the respective surface of the thinner thermoplastic foam sheet can assume any desired values (sizes), for example 30 mm. Preferably, the distance between the individual structural units of the patterned depressions is at most 20 mm (average value over the entire pattern), more preferably 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-like structure) may be arbitrary, preferably in the range of 1 to 10 mm, more preferably 2 to 6 mm.

Likewise, the depressions as such (ie the depth of a structuring) can assume any desired values (sizes). Thus, it is conceivable that in subregions of a surface the same structural units / patterns are included, but that differ in terms of their depth. The pits are (as an average) in usually not greater (less than) 25% of the corresponding panel thickness, which may be slightly higher for very thin thermoplastic foam panels (for example, less than 10 mm thick). For example, if a thin thermoplastic foam sheet has a thickness of 100 mm, the recesses (on average) preferably have a maximum depth of 20 mm.

Preferably, the patterned depressions have on average a depth of at most 5 mm, more preferably from 0.5 mm to 5 mm, even more preferably a depth of 1 to 3 mm (in each case based on the parts of the surface of the corresponding thinner thermoplastic foam sheet have no depressions). The minimum depth of a structured recess in the context of the present invention is 0.2 mm, preferably 0.3 mm, particularly preferably 0.5 mm (as averages in each case based on the parts of the surface of the corresponding thinner thermoplastic foam sheet, which have no depressions).

In one possible embodiment, two contact surfaces to be welded together with structured depressions are provided per pair of plates to be welded. In a preferred embodiment of the present invention, the two contact surfaces to be thermally welded have identical or at least 80% identical patterning pattern (pattern or structure). Preferably, the two contact surfaces to be thermally welded have identical patterning patterns. Furthermore, it is preferred that the contact surfaces to be thermally welded before being brought into contact in step c) are superimposed so that as many as possible of the structured depressions on both surfaces to be thermally welded together cover each other. Particularly preferably, two contact surfaces with identical structuring pattern are thermally welded together, wherein the contact surfaces to be thermally welded before welding are superimposed so that the structured recesses completely coincide with each other on both contact surfaces to be thermally welded.

In the context of the present invention, the structured depressions contained on the contact surfaces to be welded can assume any structures or structural forms. Preferably, the structured recesses are punctiform, linear or lattice-shaped, particularly preferably lattice-shaped. In a further embodiment, the structured depressions are preferably karoförmig, diamond-shaped, rectangular, square or lattice-shaped, more preferably grid-shaped. The patterned depressions can account for 20 to 80%, preferably 35 to 70%, more preferably 40 to 50% of the respective surface of a thinner thermoplastic foam sheet.

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 can be for example a check, a diamond, a rectangle, 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. The arrangement of the structural units preferably takes place in the form of a lattice.

The structured depressions are preferably karoförmig, diamond-shaped, rectangular, square or lattice-shaped, more preferably grid-shaped.

The process of thermal welding within the method according to the invention for producing the at least two-layer thermoplastic foam boards comprises at least steps b) and c).

At the points where the starting plates are thermally welded together, a weld is formed. In particular, when a pressing and / or reflow step with high heat input is performed within the manufacturing process, the thickness of the at least two-ply thermoplastic foam sheets as such is less than the sum of the respective thicknesses of the thinner thermoplastic foam sheets used. In the process of the invention, the length of the side of the thinner thermoplastic foam sheets, measured perpendicular to their contact surfaces (plate thickness), is preferably reduced by not more than 6%, more preferably by not more than 4.5% in the course of welding by foam loss.

Step b) comprises heating at least one thinner thermoplastic foam sheet at its contact surface having the structured depressions. The implementation of the heating as such is known in the art. The effect of the heating is achieved in the surfaces to be welded or contact surfaces by the respective contact surface is exposed to a heat source. The corresponding heat sources or devices are known to the person skilled in the art.

Preferably, the heating is carried out with a heating element selected from a heating blade, a heating grid or a heating plate, wherein the device may optionally be provided with nubs or grooves. For example, the heating may be performed continuously by using a heating blade, and a mirror welding method may be performed by using a heating plate or a heating grid. If the corresponding device for heating has nubs or grooves, in this way the structured depressions can be applied to the corresponding surface of the thinner thermoplastic foam plates to be thermally welded. Instead of using a device such as a heating blade or a heating grid, it is also possible within the scope of the present invention for the heating to be carried out partially or completely using electromagnetic radiation (see also below in the text). It is also conceivable that, following the heating by means of a heating blade or a heating grid, an additional heating step using electromagnetic radiation is connected downstream.

In a preferred embodiment, the heating is carried out with at least two heating elements on mutually parallel planes and parallel to the two thinner thermoplastic foam plates, wherein the heating element is each selected from a heat shield, a heater or a hot plate and these devices optionally provided with nubs or grooves could be. The contact surface of the at least one thinner thermoplastic foam sheet having the patterned pits is formed in step b) by at least one heating element, preferably at a temperature in the range of 150 ° C to 500 ° C, more preferably 250 ° C to 450 ° C , more preferably from 300 ° C to 400 ° C, heated.

The contact surface is preferably heated to temperatures of 50 to 300 ° C above the glass transition temperature in amorphous thermoplastic foams or from 50 to 100 ° C above the melting temperature of semi-crystalline thermoplastic foams. The contact surface of the at least one thinner thermoplastic foam sheet having the structured depressions is preferably heated in step b) for at least 0.5 seconds. The term "heating time" in the context of this invention means the period over which the thinner thermoplastic foam sheet to be welded is exposed to heat from a heating element.

The contact surface of the at least one thinner thermoplastic foam sheet having the patterned pits is preferably heated for at most 6 seconds, more preferably for at most 4 seconds, even more preferably for at most 3 seconds.

The heating is preferably carried out with the aid of at least one heating element, the distance of the at least one heating element in step b) from the at least one contact surface to be heated having the structured depressions preferably at least 0.2 mm, more preferably 0.3 to 3.0 mm , even more preferably 0.4 to 1.5mm. The step b) may comprise the steps b1), b2) and b3): b1) movement of at least one heating element from a position from which no heating is possible, in the heating position assumed by the at least one heating element in step b2) b2) heating without movement of at least one heating element, wherein each point of the contact surface to be heated is exposed to the heat of at least one heating element. b3) movement of the at least one heating element from the position according to step b2) into a position from which no more heating is possible.

The Gesamtheizzeit corresponds to the sum of the times for braking from the movement in step b1), wherein the time required for deceleration in the invention is also referred to as deceleration time, the residence of the heating element in heating position in step b2), wherein the time for the residence in the heating position in the context of the invention is also referred to as the service life and for the acceleration from the heating position according to step b3) into the movement, the time for the acceleration in the context of the invention also being referred to as the acceleration time. Preferably, the sum of the deceleration and acceleration time is 0.3 to 0.7 seconds, more preferably 0.5 seconds.

The service life is preferably 1, 1 to 2 seconds, more preferably 1, 6 seconds.

In one embodiment of the present invention, the heating takes place in the presence of at least one absorber of electromagnetic radiation (hereinafter referred to as "absorber") .At least one absorber is applied to at least one contact surface of at least one thinner thermoplastic foam sheet In the context of the present invention, application to a contact surface with structured depressions is carried out in such a way that the absorber is not applied to the recessed part (ie not into the recesses) of the corresponding contact surface two thinner thermoplastic foam plates an absorber is applied only on one of the two contact surfaces to be welded thermally, this can for example also take place on a contact surface, which has no depressions em plate pair applied to only one contact surface of the thinner thermoplastic foam sheets at least one absorber of electromagnetic radiation. In this case, the absorber is preferably applied to a contact surface of at least one of the thinner thermoplastic foam plates with structured depressions, in particular the absorber is not applied to the recessed part of the corresponding contact surface. Methods for applying the absorber of electromagnetic radiation are known in the art, for example, the absorber can be applied over a large area to the corresponding contact surface of the thinner thermoplastic foam sheet. The absorber is preferably used by electromagnetic radiation as a dispersion, in particular as an aqueous dispersion. The application to the contact surface can be done for example by brushing, knife coating, rolling, spraying or printing.

The amount of absorber (solid) on a contact surface is normally 0.01 g / m ² to 00 g / m ² , preferably 0.1 g / m ² to 50 g / m ² . Particularly preferably 1 g / m ² to 20 g / m ² . The absorbers can be applied on one side or on both sides.

Absorbers of electromagnetic radiation as such are known to those skilled in the art. Suitable susceptors for radio frequency radiation are described in WO 2006/050013, WO 99/47621 and WO 012/1725. Preferred susceptors are polymeric ionomers. Absorbers of other types of radiation are described, for example, in WO 2009/071499 on pages 9 to 11. 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 by using microwave rays, it is preferable to select an electromagnetic radiation absorber having a good absorption ability in the microwave wavelength range. Suitable absorbers are, for example, organic IR absorbers, organic microwave absorbers, inorganic IR absorbers or inorganic microwave absorbers.

For the purposes of this application, IR absorber is to be understood as meaning a compound which, applied in a layer thickness of <50 μm, exhibits an absorption s of 90% at at least one wavelength of radiation of the wavelength range from 700 nm to 1000 μm. Preferably, the wavelength range of> 1 μηι to 20 ym.

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.

If, in the context of the present invention, at least one contact surface of at least one thinner thermoplastic foam board is applied with at least one absorber of electromagnetic radiation, thermal welding preferably takes place partially or completely using electromagnetic radiation. The person skilled in the art knows the apparatus 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.

In a preferred embodiment of the present invention, at least one contact surface of at least one thinner thermoplastic foam sheet is applied with at least one absorber of electromagnetic radiation, wherein at least one thinner thermoplastic foam sheet to which the absorber has been applied by electromagnetic radiation electromagnetic radiation is irradiated. Preferably, the absorber is not applied to the recessed part (ie, not into the recesses) of the corresponding contact surface. As already mentioned above, in addition to the absorber of electromagnetic radiation, it is also possible to apply further substances with other use properties together with the absorber to the contact surface of the corresponding thinner thermoplastic foam boards. Suitable further substances may be, for example, binders, flame retardants, pH regulators and, if appropriate, solvents. Binders, flame retardants, pH regulators and solvents as such are known to the person skilled in the art.

In one embodiment of the present invention, a mixture comprising at least one absorber of electromagnetic radiation, ii) at least one binder and / or iii) at least one flame retardant is applied to at least one contact surface of at least one thinner thermoplastic foam sheet.

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 step c), the contact surfaces of the at least two thinner thermoplastic foam sheets are brought into contact to form a weld. Preferably, in step c) at least one of the two thinner thermoplastic foam sheets is pressed with its contact surface against the contact surface of the respective other thinner thermoplastic foam sheet, preferably at a pressure of 0.1 to 5 bar.

The contact surfaces are pressed against one another generally in the second to minute range. Step c) is performed after step b).

As a rule, the weld has a lower tensile strength at locations where structured recesses are introduced into the contact surface of at least one thinner thermoplastic foam board than at locations without structured depressions.

Preferably, the at least two-day thermoplastic foam sheet obtained by welding has a tensile strength of at least 0.1 N / mm ² , more preferably at least 0.14 N at each point, measured perpendicular to the contact surface of the thinner thermoplastic foam sheets and / or the weld. mm ² , more preferably at least 0.2 N / mm ² .

Preferably, the tensile strength of the weld at the sites of patterning is 10 to 80%, more preferably 35 to 75%, of the tensile strength as compared to sites without patterning.

The tensile strength of the weld at the points without structuring is at least 0.13 N / mm ² to 1 N / mm ² . The weld may in principle assume any thickness at any point, preferably between 20 and 350 μm (average value distributed over at least five measuring points determined by light microscopy), more preferably between 50 and 200 μm, in particular between 80 and 130 μm.

Step c) is carried out not later than 2 seconds, preferably less than 1 second and even more preferably less than 0.5 seconds, in particular less than 0.2 seconds after the completion of step b). As part of the welding operation, a reduction in the plate thickness of the thinner thermoplastic foam sheets may occur due to foam loss. In the method according to the invention, the length of the side becomes thinner Thermoplastic foam sheets, measured perpendicular to their contact surfaces (plate thickness), in the course of welding by foam loss preferably by not more than 10%, more preferably reduced by not more than 6%. The method may comprise a further step d), carried out before step a), in which first of all the foaming skin, preferably by milling, is removed from the contact surfaces of the thinner thermoplastic foam boards which are to be thermally welded together. If, in the context of the present invention, surfaces of thinner thermoplastic foam boards are thermally welded, which are not provided with structured depressions, the corresponding surfaces can be, for example, planar (still provided with a foaming skin) or free from foaming skin. In the context of the present invention, the term "foaming skin-free" is understood to mean that the foaming skin produced during the production process of the respective thermoplastic foam board is removed, for example, by planing or milling.

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 the context of the welding operation comprising at least steps b) and c), a reduction in the plate thickness of the thinner thermoplastic foam sheets may occur due to foam loss. In the process of the present invention, the length of the side of the thinner thermoplastic foam sheets measured perpendicular to their contact surfaces (plate thickness) is preferably reduced by not more than 10%, more preferably by not more than 6% in the course of welding by foam loss.

In one embodiment of the present invention, the thermoplastic foam sheets of the invention contain at least one flame retardant. Flame retardants as such are known in the art. Preferred flame retardants in the context of the present invention are selected from a phosphate, a phosphite, a phosphonate, a polyphosphonate, an amine, a metal oxide hydrate, in particular an aluminum oxide hydrate or a halogenated organic compound. The abovementioned flame retardants, preferably the phosphorus-containing flame retardants but not the halogenated organic compounds, are preferably applied directly to at least one surface (per pair of plates) of the starting plates to be welded prior to thermal welding. Preferred phosphates and phosphonates are selected from D MP (dimethymethylphosphonate), DMPP (dimethylpropyl 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).

Preferred halogenated organic compounds are bromine-containing organic compounds, particularly preferred are HBCD (hexabromocyclododecane) or brominated polystyrenes. Brominated polystyrenes are commercially available, for example from Emerald, Great Lakes. They are preferably used in amounts of 0.5 to 5 wt .-% (based on the starting plate). If halogenated organic compounds are used as flame retardants, this is preferably done during the production process of the starting plates, that is, the flame retardant is evenly distributed over the entire thickness of the respective starting plate.

A particularly preferred flame retardant is dimethylpropylphosphonate (DMPP), which is commercially available, for example, under the name Levagard DMPP from Lanxess. In one embodiment of the present invention, expandable graphite is preferred, which can also be used as an absorber.

Optionally, in the process of the invention, a drying step may be carried out, for example after an absorber of electromagnetic radiation has been applied to the surface of the thinner thermoplastic foam boards. Drying normally takes place for a period of 10 minutes to 2 hours and / or at a temperature in the range of 50 to 100 ° C.

The method may comprise a further step d), carried out before step a), in which first of all the foaming skin, preferably by milling, is removed from the contact surfaces of the thinner thermoplastic foam boards which are to be thermally welded together.

The method may comprise a further step e), in which the at least two thinner thermoplastic foam sheets are aligned at a distance a parallel to one another, so that they form a gap and the contact surfaces, of which at least one structured recesses, are opposite, preferably Distance a 20 to 100 mm, more preferably the distance a is 30 to 50 mm. Step e) is preferably carried out before step b). In one embodiment, the method comprises step e), which is performed before step b), and in step b) into the space between the two thinner thermoplastic foam plates, the at least two heating elements on mutually parallel planes and parallel to the two thinner thermoplastic foam plates whose contact surfaces are opposite, introduced, wherein the contact surfaces of the two thinner thermoplastic foam plates and the heating elements do not touch each other. In this embodiment, in step b), the heating elements are preferably completely removed from the intermediate space after 6 seconds at the latest.

Another object of the invention is a thermoplastic foam sheet, which is at least two days, can be prepared according to the above-described method of the invention.

The invention will be clarified by way of examples below.

1. Preparation of the thinner thermoplastic foam sheets to be welded

The tests are carried out with thinner thermoplastic foam boards made of Styrodur® 4000 CS (commercial product of BASF SE / starting plates), the dimensions 1300x660 mm, which have a thickness of 60 mm, a density of about 38 g / l. On both sides of the extruded sheets, the foaming skin is removed, so that these sheets each have a thickness of 53 mm at each point, just prior to the welding and / or the introduction of the structured depressions. After welding, the plate is finished to your sales dimensions (length and width).

Examples 3 to 5: Of two thin thermoplastic foam sheets to be welded, a rectangular pattern is milled into the foam-skin-free surface of a plate, which is produced by grooves being cut into the surface at a defined distance in both the longitudinal and transverse direction of the plates. The distance and the width of the grooves are varied (see Table 1). The depth of the grooves is 2.0 mm. The surface of the foam sheet having the milled pattern forms the contact surface with the sheet to be welded.

Examples 6 and 8: In two further examples, in the case of two thinner thermoplastic foam sheets to be welded, the foam-skin-free surfaces are used Both plate milled a rectangular pattern, which is created by the fact that both longitudinally and in the transverse direction of the plates grooves are milled in a defined distance in the surface. The spacing of the grooves is 12 mm, the width of the grooves 5 mm. The groove depth on both plates is 1, 0 mm.

The thinner thermoplastic foam sheets are then welded so that the grooves on one side are aligned with the grooves on the other side. Example 7: In another example, when two thinner thermoplastic foam sheets to be welded are cut into the foam-skin-free surface of one sheet, only grooves in the longitudinal direction of the sheet are milled into the foam-skin-free surface of the other sheet. The distance between the grooves is 12 mm, the groove width 5 mm. The depth of the longitudinal grooves is 2 mm, the transverse grooves also 2 mm.

In Examples 1 and 2, a pattern or a different type of recess is not milled into any of the thinner thermoplastic foam sheets to be welded, but the welding is carried out analogously to the examples mentioned above. For differences concerning the welding process itself, see the following section, 2. Welding.

2. Welding The thinner thermoplastic foam boards prepared in accordance with the above examples for the respective examples are thermally welded in a welding installation.

In the welding plant receiving plates are provided, which can accommodate the to be welded thinner thermoplastic foam sheets, according to Examples 1 to 8, in the dimensions 1300 x 660 mm. The receiving plates and to be welded thinner thermoplastic foam sheets are arranged vertically. Two heating elements of dimension 1320 680 mm are heated to a welding temperature of 350 ° C. The heating is done contactless by IR emitters, but can also be done by inductive heating.

From the heating stations, the heating elements are moved into the space between the plates to be welded. The heating elements are first accelerated and then braked again, so that the heating elements in the middle in front of the welding plates remain standing. There the heating elements stay for a defined service life.

The distance between the heating elements and the plates to be welded is 0.7mm.

For Examples 1 and 3 to 8, the service life is 1, 6 seconds, plus the time during the deceleration and acceleration process of 0.5 seconds, so that the contact surfaces of the plates to be welded heated in total over a period of 2.1 seconds become. ,

In Example 2, the life in the context of welding but deviating from the other examples, 2.1 seconds, so that the contact surfaces of the plates to be welded are heated in total over a period of 2.6 seconds.

At the end of the service life, the heating elements are accelerated again and leave the space between the plates to be welded. The heating elements are metal plates with the above dimensions of 1320 x 680 mm.

After the heating elements have left the gap between the plates to be welded, they are pressed together. Both mounting plates move towards each other and press the plates to be welded together with a defined contact pressure.

The difference in time between the completion of leaving the gap by the heating elements and the compression is 0.2 seconds in Examples 1 to 7, in contrast, 3 seconds in Example 8. 3. Determination of tensile strength and foam loss

To obtain the averages, standard deviation and minimum tensile strength value of the weld, corresponding to the value of the sample with the lowest measured weld tensile strength, are prepared from a thermoplastic two-ply foam sheet obtained by welding two thinner thermoplastic foam sheets according to the examples 1 to 8, 20 samples of dimension 100 x 100 mm x (thickness of the two-ply foam plastic sheeting plate) cut (Fig. 1). The tensile strength perpendicular to the plate plane is analogous to DIN EN 1607; (2013) on these samples. The plates on which the tensile strengths are measured are produced from the welded plates by a processing step in which the sides of the plates are milled in order to reduce them to the sales dimensions. FIG. 1 in this context illustrates the exact positions of the sampling on the respective two-layered thermoplastic foam sheet, viewed perpendicular to the weld, or to the contact surface of the welded thinner thermoplastic foam sheets. The foam loss in mm is determined by measuring and subtracting the side length of the respective thinner thermoplastic foam sheet perpendicular to the contact surface of the thinner thermoplastic foam sheets, before and after welding.

4. Measurement results

Table 1: Measurement results for the welding of thinner thermoplastic foam boards; Examples 1, 2 and 8 are comparative examples, examples 3 to 7 are according to the invention.

Loss of foam for both thinner thermoplastic foam panels, corresponding to a foam loss of 2.2 mm for each of the two thinner thermoplastic foam panels. Foam loss reduction per thinner thermoplastic foam sheet: 4.1%

² Foam loss for both thinner thermoplastic foam panels, corresponding to a foam loss of 3.4 mm for each of the two thinner thermoplastic foam panels. Foam loss reduction per thinner thermoplastic foam sheet: 6.4%

³ The contact pressure is determined by the force with which the foam sheets are compressed, divided by the area of the foam sheets with the dimensions 1300 mm x 660 mm The examples show that the minimum tensile strength of two-ply thermoplastic foam sheets obtained by welding thinner thermoplastic foam sheets having no patterned pits, with the same foam loss, is significantly lower (<0.1 N / mm ² ) as such be obtained from thinner thermoplastic foam sheets, of which at least one thinner thermoplastic foam sheet contains structured recesses (see Examples 3 to 7 with Comparative Example 1).

Only with increased foam loss (Comparative Example 2, 6.8 mm instead of 4.4 mm in the other examples) comparable values for the minimum tensile strength can be observed. In addition, the tensile strength of the weld seam of Examples 3 to 7 according to the invention overall is significantly more homogeneous than in the comparative examples, such as their consistently lower standard deviations for the tensile strength (Examples 3 to 7, 0.11 to 0.19 N / mm ² ; , 29 and 0.32 N / mm ² in Comparative Examples 1 and 2).

If the time between the completion of the heating step b), and the contact surfaces to be welded according to step c), as in the non-inventive example 8, more than 2 seconds, no weld is formed at points with structured recesses. As a result, the lowest tensile strength (minimum tensile strength) measured on the 20 samples taken from the obtained two-ply thermoplastic foam sheet decreases to zero.

Claims

claims

A process for producing at least two-ply thermoplastic foam sheets by thermally welding at least two thinner thermoplastic foam sheets to the at least two-ply thermoplastic foam sheet comprising steps a), b), c):

Introducing structured depressions into at least one contact surface of at least one of the thinner thermoplastic foam boards,

Heating at least one thinner thermoplastic foam sheet at its contact surface having the patterned depressions, contacting the contact surfaces of the at least two thinner thermoplastic foam sheets to form a weld, wherein step c) is performed no later than 2 seconds after the completion of step b) ,

2. The method according to claim 1, characterized in that the length of the side of the thinner thermoplastic foam sheets, measured perpendicular to their contact surfaces, in the course of welding by foam loss by not more than 6%, preferably not more than 4.5% is reduced ,

3. The method according to any one of claims 1 to 2, characterized in that i) the structured depressions on average have a depth of at most 5 mm, preferably 0.5 mm to 5 mm, more preferably 1 to 3 mm, and / or the width of a structural unit is in the range from 1 to 10 mm, preferably from 2 to 6 mm, and / or the distance between the individual structural units of the structured depressions is on average not more than 20 mm, preferably 7.5 to 20 mm, and / or iv) the structured depressions are karo-shaped, diamond-shaped, rectangular, square-shaped or grid-shaped, preferably grid-shaped.

4. The method according to any one of claims 1 to 3, characterized in that i) the weld at points at which in the contact surface of at least one thinner thermoplastic foam plate structured recesses are introduced, a lower tensile strength than at

Positions without structured depressions, and / or the at least two-ply thermoplastic foam sheet at any point, measured perpendicular to the contact surface of the thinner thermoplastic foam sheets and / or the weld, a tensile strength of at least 0.1 N / mm ² , preferably of at least 0.14 N. / mm ² , more preferably at least 0.2 N / mm ² , and / or the thickness of the weld is 20 and 350 μm, and / or the tensile strength of the weld at the structuring sites is 10 to 80%, preferably 35 to 75% of the tensile strength compared to non-patterned sites, and / or the weld tensile strength at the non-patterned sites is at least 0.13 N / mm ² to 1 N / mm ² .

5. The method according to any one of claims 1 to 4, characterized in that the structured recesses 20 to 80%, preferably 35 to 70%, make up the respective contact surface of the thinner thermoplastic foam sheet.

6. The method according to any one of claims 1 to 5, characterized in that the method additionally comprises a step e), which is preferably carried out before step b), wherein in step e) the at least two thinner thermoplastic foam sheets at a distance a parallel to each other be aligned so that they form a gap and the contact surfaces, of which at least one structured recesses, opposite, preferably, the distance a is 20 to 100 mm, more preferably the distance a is 30 to 50 mm.

7. The method according to any one of claims 1 to 6, characterized in that i) the contact surface of the at least one thinner thermoplastic foam sheet having the structured recesses, in step b) by at least one heating element having a temperature in the range of 150 ° C. to 500 ° C, preferably from 250 ° C to 450 ° C, even more preferably from 300 ° C to 400 ° C, heated, and / or ii) the contact surface of the at least one thinner thermoplastic foam sheet having the patterned pits is heated in step b) for at least 0.5 seconds, and / or iii) the heating is carried out by means of at least one heating element, the distance of the at least one heating element in step b) is at least 0.2 mm, preferably 0.3 to 3.0 mm, more preferably 0.4 to 1.5 mm, of the at least one contact surface to be heated, which has the structured depressions, and / or iv) step c) is carried out not later than 1 second, preferably not later than 0.5 seconds, in particular not later than 0.2 seconds after the completion of step b), and / or v) the method comprises the step e ), which is carried out before step b), and in step b) in the space between the two thinner thermoplastic foam plates, the at least two heating elements on parallel to each verse at the bottom and parallel to the two thinner thermoplastic foam sheets whose contact surfaces are opposite each other, with the contact surfaces of the two thinner thermoplastic foam sheets and the heating elements not touching each other, and / or the method comprising step e) preceding step b ) is carried out, and in step b) the heating elements are completely removed again at the latest after 6 seconds again from the intermediate space.

8. The method according to any one of claims 1 to 7, characterized in that the step b) comprises at least the steps b1), b2) and b3): b1) movement of at least one heating element from a position from which no heating is possible b2) heating without movement of at least one heating element, each point of the contact surface to be heated being exposed to heat from at least one heating element, b3) movement of the at least one heating element from the position according to step b2) into a position from which no more heating is possible, wherein the total heating time corresponds to the sum of the times for deceleration from the movement in step b1), the retention of the heating element in the heating position according to step b2) and for the acceleration from the heating position according to step b3) into the movement.

9. The method according to any one of claims 1 to 8, characterized in that the thinner thermoplastic foam sheet is a particle foam or an extrusion foam, preferably an extrusion foam of polystyrene or of a copolymer produced from styrene.

10. The method according to any one of claims 1 to 9, characterized in that i) to be welded pair of plates in step a) both thermally welded contact surfaces are provided with structured recesses, and / or ii) the two thermally welded contact surfaces identical or have at least 80% matching pattern structuring, preferably wherein the contact surfaces to be thermally welded before the in

Bringing the contact in step c) are superimposed so that as many of the structured wells on both sides to be thermally welded together to cover each other.

11. The method according to any one of claims 1 to 10, characterized in that i) the heating in step b) is carried out with a heating element selected from a heat shield, a heater or a hot plate, wherein the device may optionally be provided with nubs or grooves or ii) the heating in step b) is carried out with at least two heating elements on mutually parallel planes and parallel to the two thinner thermoplastic foam boards, wherein the

Each heating element is selected from a heat shield, a heater or a hot plate and these devices may optionally be provided with knobs or grooves.

12. The method according to any one of claims 1 to 11, characterized in that at least one contact surface of at least one thinner thermoplastic foam plate at least one absorber of electromagnetic radiation is applied, wherein at least one thinner thermoplastic foam sheet on which the absorber was applied by electromagnetic radiation, is irradiated with electromagnetic radiation.

13. The method according to any one of claims 1 to 12, characterized in that the heating in step b) at temperatures of 50 to 300 ° C above the glass transition temperature at amorphous thermoplastic foams or from 50 to 100 ° C above the melting temperature in semi-crystalline thermoplastic foams is carried out, and / or in step c) at least one of the two thinner thermoplastic

Foam plates is pressed with its contact surface against the contact surface of the respective other thinner thermoplastic foam sheet. 14. The method according to any one of claims 1 to 13, characterized in that the method comprises a further step d), carried out before step a), in which of the contact surfaces of the thinner thermoplastic foam sheets to be thermally welded together in one first step, first the foaming skin, preferably by milling, is removed.

Method according to one of claims 1 to 14, comprising at least one further step e) e) the at least two thinner thermoplastic foam sheets are aligned at a distance a parallel to each other, so that they form a gap and the contact surfaces, of which at least one structured depressions Preferably, the distance a is 20 to 100 mm, more preferably the distance a is 30 to 50 mm, wherein step e) is performed before step b).

16. Thermoplastic foam sheet, which is at least two layers, can be produced by a method according to any one of claims 1 to 15.