Method for producing thermoplastic foam panels by means of at least two heating elements offset in parallel with each other

Abstract

The present invention relates to a process for the production of at least two-layer thermoplastic foam sheets via thermal welding of at least two thinner thermoplastic foam sheets. In the process of the invention, at least two heating elements are conducted on mutually offset planes between the surfaces to be welded of the thinner thermoplastic foam sheets, and the foam sheets here do not touch the heating elements. The number of layers of the thermoplastic foam sheet is per se a result of the number of thinner thermoplastic foam sheets that are thermally welded to one another. If by way of example three thinner thermoplastic foam sheets are thermally welded to one another, a three-layer thermoplastic foam sheet is per se obtained, and if there are four thinner thermoplastic foam sheets the result is accordingly per se a four-layer thermoplastic foam sheet.

Claims

1. A process for the production of an at least two-layer thermoplastic foam sheet via thermal welding of at least two thinner thermoplastic foam sheets, comprising the following steps a) to e): a) two thinner thermoplastic foam sheets are oriented parallel to one another with a separation a, in such a way that they form an intermediate space, b) at least two heating elements are introduced on parallel-offset planes, and parallel to the two thinner thermoplastic foam sheets, into the intermediate space, and the surfaces of the two thinner thermoplastic foam sheets here do not touch the heating elements, c) the heating elements are introduced between the two thinner thermoplastic foam sheets to an extent such that, in relation to every location on the respective surface of the two thinner thermoplastic foam sheets, at least one of the heating elements has been present at least temporarily between the two thinner thermoplastic foam sheets, d) the heating elements are removed completely from the intermediate space, e) at least one of the two thinner thermoplastic foam sheets is forced against the surface of the respective other thinner thermoplastic foam sheet where, in step b), two heating elements are introduced from, in each case, mutually opposite directions into the intermediate space or, in step d), two heating elements are in turn removed in, in each case, mutually opposite directions from the intermediate space.

2. The process according to claim 1, wherein the thickness of the weld formed via the thermal welding process is from 30 to 200 m.

3. The process according to claim 2, wherein the thickness is from 80 to 100 m.

4. The process according to claim 1, wherein the thinner thermoplastic foam sheet is a molded foam or an extruded foam.

5. The process according to claim 4, wherein the thinner thermoplastic foam sheet is an extruded foam made of polystyrene or made of a copolymer produced from styrene.

6. The process according to claim 1, wherein the thermoplastic foam sheet comprises at least one flame retardant.

7. The process according to claim 6, wherein the flame retardant is selected from a phosphate, a phosphite, a phosphonate, a polyphosphonate, melamine, an aluminum oxide hydrate, or a halogenated organic compound.

8. The process according to claim 1, wherein two heating elements are used, or the heating elements are heating plates.

9. The process according to claim 8, wherein the two heating elements are IR sources with surface temperature from 200 to 1000 C.

10. The process according to claim 1, wherein, in each sheet pair to be welded, at least one and preferably both of the surfaces to be thermally welded of the thinner thermoplastic foam sheets are foaming-skin-free.

11. The process according to claim 1, wherein the thermal welding process is carried out at temperatures which are from 50 to 300 C. above the glass transition temperature in the case of amorphous thermoplastic foams, or which are from 50 to 100 C. above the melting point in the case of semicrystalline thermoplastic foams.

12. The process according to claim 1, wherein the heating elements in the steps b) and d) are moved with a velocity of from 0.1 to 5 m/s.

13. The process according to claim 1, wherein, in step b), two heating elements are introduced from respectively mutually opposite directions into the intermediate space, and, in step d), two heating elements are removed in respectively mutually opposite directions from the intermediate space.

14. The process according to claim 1, wherein the total duration of the steps b) to e) is at most 20 seconds.

15. The process according to claim 1, wherein, in step a), the length (x-direction) of the two thinner thermoplastic foam sheets is respectively from 500 to 2800 mm, and their width (y-direction) is from 500 to 1250 mm, and their thickness (z-direction) is from 20 to 200 mm.

16. The process according to claim 1, wherein the length (x-direction) of the heating elements is respectively the same as or at most 10% greater than the corresponding lengths (x-direction) of the two thinner thermoplastic foam sheets, and the width (y-direction) of the heating elements is from 30 to 100% of the corresponding width (y-direction) of the two thinner thermoplastic foam sheets.

17. The process according to claim 1, wherein the heating elements are moved parallel to the xy-plane and along the y-direction (width) of the two thinner thermoplastic foam sheets.

18. The process according to claim 1, wherein the density of the thermoplastic foam sheets is from 10 to 500 g/l.

19. The process according to claim 1, wherein the process is carried out in a thermally insulated enclosure, and a temperature that is constant within +/10 C. is maintained in the range from 40 to 200 C. in the thermal enclosure.

20. The process according to claim 1, wherein, in the steps b) to d), the separation between the surface of each of the two thinner thermoplastic foam sheets and the surface of the respective heating element that is respectively spatially closest thereto is from 0.5 to 25 mm.

21. The process according to claim 1, wherein in step b), two heating elements are introduced from, in each case, mutually opposite directions into the intermediate space and, in step d), two heating elements are in turn removed in, in each case, mutually opposite directions from the intermediate space.

Description

(1) The invention is illustrated below by examples.

(2) In all of the examples the thinner thermoplastic foam sheets (starting sheets) are produced in the continuous extrusion process described in Polystyrol, Kunststoffhandbuch 4 [Polystyrene, plastics handbook 4] [H. Gausepohl and R. Gellert, Hanser-Verlag Munich (1996)], in chapter 13.2.3 (pp. 591-598), in particular in figure 13.24, upper part. In each case, two starting sheets (Styrodur 3035 CS, density 35 g/l, thickness 50 mm, size (lengthwidth) 12050 cm.sup.2) were welded with the use of two heating elements two weeks after said sheets had been produced. In the case of the examples using starting sheets having no foaming skin, the foaming skin was removed from the starting sheets about 24 hours before the welding process by planing 3 mm from the surface to be welded. The thickness of the starting sheets is then about 47 mm.

(3) Table 1 below provides a more detailed description of the processes used for the various experiments. The expression introduction of the two heating elements means the introduction of the two heating elements into the intermediate space between the two thinner thermoplastic foam sheets. The expression removal of the two heating elements means the removal of the two heating elements from the intermediate space between the two thinner thermoplastic foam sheets.

(4) TABLE-US-00001 TABLE 1 Removal of the Exper- Surface of the Introduction of the two heating iment two starting sheets two heating elements elements 1a with foaming on mutually offset planes with retention skin from opposite direction of direction 1b with foaming on mutually offset planes with reversal skin from opposite direction of direction 2a without foaming on mutually offset planes with retention skin from opposite direction of direction 2b without foaming on mutually offset planes with reversal skin from opposite direction of direction 3 without foaming on one plane from with reversal (comp.) skin opposite direction of direction 4a without foaming on mutually offset planes with retention (comp.) skin from same direction of direction 4b without foaming on mutually offset planes with reversal (comp.) skin from same direction of direction comp. in table 1 and in table 2 means comparative example

(5) The thickness of the weld is determined by using a scopeEye digital incident-light microscope with approximately 60 magnification.

(6) The welded two-layer thermoplastic foam sheets are tested for tensile strength in the plane of the sheet in accordance with DIN EN 1607: 2013-05, and for fire performance to B2 in accordance with DIN 4102-1: 1998-05. Flame application in the fire test occurs directly at the weld.

(7) All of the values measured are tested at three positions on the welded two-layer thermoplastic foam sheets. The distance of each of the three positions from the edge of the foam sheets, in the direction of the width of the welded two-layer thermoplastic foam sheets, was 250 mm. The following applies to the three positions in the direction of the length of the foam sheets: Position 1: distance 200 mm from one edge of the foam sheets and 1000 mm from the other edge of the foam sheets Position 2: distance 400 mm from position 1; this corresponds to a distance of 600 mm from both edges of the foam sheets Position 3: distance 400 mm from position 2 and therefore 800 mm from position 1; this corresponds to a distance of 1000 mm from one edge of the foam sheets and 200 mm from the other edge of the foam sheets

(8) TABLE-US-00002 TABLE 2 Position 1 Position 2 Position 3 Tensile Tensile Tensile strength Thickness of B2 test strength Thickness of B2 test strength Thickness of B2 test Experiment (N/mm.sup.2) weld (m) (DIN 4102) (N/mm.sup.2) weld (m) (DIN 4102) (N/mm.sup.2) weld (m) (DIN 4102) 1a 0.17 200 passed 0.20 180 passed 0.17 200 passed 1b 0.16 190 passed 0.05 190 passed 0.15 170 passed 2a 0.17 160 passed 0.16 130 passed 0.18 140 passed 2b 0.16 150 passed 0.1 160 passed 0.18 170 passed 3 0.12 220 failed 0.05 250 failed 0.18 300 failed (comp.) 4a 0.12 400 failed 0.1 300 failed 0.13 250 failed (comp.) 4b 0.13 350 failed 0 500 failed 0.09 300 failed (comp.)

(9) Inventive examples 1a, 1b, 2a, and 2b clearly show that a technical effect results from the introduction of at least two heating elements on parallel-offset planes from mutually opposite directions in the intermediate space between the two thinner thermoplastic foam sheets. The weld in the inventive examples is thinner than the welds obtained with the processes described in the prior art (comparative examples 3, 4a and 4b). The at least two-layer thermoplastic foam sheets produced in the invention moreover pass the B2 fire test in accordance with DIN 4102-1: 1998-05. Furthermore, the process of the invention generally achieves higher tensile strength values.