METHOD FOR PRODUCING SANDWICH COMPONENTS

Abstract

The invention relates to a sandwich component composed of at least two building material plates which are arranged essentially parallel to one another at a distance from one another and have a polyurethane foam core between the spaced building material plates, wherein the ratio of the greatest measured compressive modulus of the polyurethane foam core in a direction oriented parallel to the building material plates to the compressive modulus of the polyurethane foam core in a direction oriented perpendicular to the building material plates is less than 1.7. To produce the sandwich components, a mixture of (a) at least one polyisocyanate component, (b) at least one component which comprises at least one polyfunctional compound which is reactive toward isocyanates and (c) at least one blowing agent is introduced by the high-pressure injection method into a hollow space between spaced building material plates. The process makes it possible to produce sandwich components whose foam core has reduced anisotropy combined with good insulation values.

Claims

1. A sandwich component comprising at least two building material plates which are arranged essentially parallel to one another at a distance from one another and have a polyurethane foam core between the spaced building material plates, wherein the ratio of the greatest measured compressive modulus of the polyurethane foam core in a direction oriented parallel to the building material plates to the compressive modulus of the polyurethane foam core in a direction oriented perpendicular to the building material plates is less than 1.7.

2. The sandwich component according to claim 1, wherein the core density of the polyurethane foam core is in the range from 20 to 100 kg/m.sup.3.

3. The sandwich component according to claim 1, wherein at least one of the building material plates is provided at least partly with a primer on the side facing the polyurethane foam core.

4. The sandwich component according to claim 1, wherein the building material plates are made of concrete, geopolymers or gypsum plaster.

5. The sandwich component according to claim 1, wherein the fresh foam of the sandwich component has a thermal conductivity in the range from 16 to 30 mW/m.Math.K.

6. A process for producing sandwich components comprising at least two building material plates which are at a distance from one another and have a polyurethane foam core, comprising the following steps: A) mixing of (a) at least one polyisocyanate component, (b) at least one component which comprises at least one polyfunctional compound which is reactive toward isocyanates and (c) at least one blowing agent by the high-pressure injection process to form a mixture; and B) introducing the mixture obtained into a hollow space between the spaced building material plates, where the compaction of the foam is in the range from 1.1 to 2.5, where the compaction is the ratio of the density of the foam in the hollow space divided by the density of the free-foamed foam body.

7. The process according to claim 6, wherein the mixing of the components (a) to (c) is carried out in a mixing chamber at a pressure of at least 100 bar.

8. The process according to claim 6, wherein the blowing agent is selected from C.sub.3-C.sub.5-alkanes, C.sub.4-C.sub.6-cycloalkanes, di-C.sub.1-C.sub.4-alkyl ethers, methyl formate, formic acid, acetone, fluorohydrocarbons, partially halogenated fluoroolefins, chlorofluorocarbons, carbon dioxide, water and mixtures of two or more thereof.

9. The process according to claim 6, wherein at least one catalyst for the reaction of the polyisocyanate component with the polyol component is added in step A).

10. The process according to claim 6, wherein the amount of the mixture introduced into the hollow space in step B) is such that the overall injected foam density is less than 100 kg/m.sup.3, where the overall injected foam density is the total amount of mixture from step A) which is introduced divided by the total volume of the hollow space to be filled with foam.

11. The process according to claim 6, wherein the amount of mixture introduced into the hollow space in step B) is in the range from 0.1 to 8 kg/s.

12. The process according to claim 6, wherein at least one of the building material plates is provided at least partly with a primer on the side facing the hollow space.

13. The process according to claim 12, wherein the primer is based on a physically setting binder and/or a chemically curing binder.

14. The process according to claim 13, wherein the primer is based on a binder selected from among an epoxy resin, post-crosslinking acrylate dispersions or post-crosslinking alkyd resin dispersions.

15. The process according to claim 12, wherein the primer is applied in an amount in the range from 20 to 600 g/m.sup.2.

16. The process according to claim 6, wherein the building material plates are made of concrete, geopolymers or gypsum plaster.

17. The sandwich component according to claim 1, wherein the fresh foam of the sandwich component has a thermal conductivity in the range from 22 to 28 mW/m.Math.K.

18. The process according to claim 6, wherein the mixing of the components (a) to (c) is carried out in a mixing chamber at a pressure in the range from 100 bar to 300 bar.

19. The process according to claim 6, wherein the amount of the mixture introduced into the hollow space in step B) is such that the overall injected foam density is less than 80 kg/m.sup.3.

Description

[0089] The accompanying figures and the following examples illustrate the invention.

[0090] FIG. 1 shows a definition of the directions in space which are employed for defining the PU foams.

[0091] FIG. 2 shows load-displacement curves of various sandwich elements.

[0092] With regard to FIG. 1, two building material plates are arranged at a distance from one another and substantially parallel to one another so that a hollow space which accommodates the foam core is present between the plates. Here, x denotes a direction which is oriented perpendicular to the building material plates, z denotes the rise direction of the foam and y denotes a direction which is oriented parallel to the building material plates and perpendicular to the rise direction.

EXAMPLE 1

[0093] In the following examples, an epoxy primer or in example d) a PU primer was used as primer. The primer was in all experiments applied manually to the concrete (brush or roller) and dried overnight before the PU reaction mixture was introduced.

[0094] The polyurethane foam (PU foam) used had a proportion of closed cells of 91% and was in each case produced on the basis of polymeric MDI and polyether polyol and water and/or HFC 245FA (1,1,1,3,3-pentafluoropropane) as blowing agent.

[0095] The following concretes were used:

[0096] Concrete 1: Based on cement (CEM I 52.5 R); compressive strength 55 MPa.

[0097] Concrete 2: Based on cement (CEM I 32.5 N); compressive strength 29 MPa.

[0098] Concrete 3: Based on cement (CEM III/B 42.5 NW/MS/NA); compressive strength 81.9 MPa

[0099] The compressive strengths (in a direction oriented perpendicular to the building material plates) were determined in accordance with DIN EN 1048.

[0100] a) CO.sub.2 Diffusion with and without Primer

[0101] For this test, concrete cubes having an edge length of 15 cm and concrete prisms (121236 cm.sup.3) were produced from concrete 1.

[0102] The CO.sub.2 diffusion/carbonatization was carried out at a CO.sub.2 content of 4%, a relative humidity of 57% and a temperature of 20 C. using a method based on the Swiss standard SN 505 262/1 (appendix I). These values are actively regulated in a carbonatization chamber. The preliminary storage of the test specimens according to this standard after removal from the formwork was storage in water up to the 3.sup.rd day and then storage at 20 C. and 57% relative humidity for 25 days. The reason for this is to allow the concrete to dry during this conditioning and not too much moisture is thus introduced into the carbonatization chambers. 500 g/m.sup.2 of the epoxy primer were applied to half of the test specimens.

[0103] To determine the carbonatization depth, a slice was split off from the prisms and the new fracture surface was sprayed with phenolphthalein. The carbonatized region does not discolor, while the region which has not been carbonatized takes on a pink color. The carbonatization depth is determined at five places on each side of the prism. This gives 20 measurements per age. The carbonatization depth is determined before the test specimens are placed in the chambers and also after 7, 28 and 63 days. Because the mortar carbonatizes very quickly, the carbonatization depth was determined there after 0, 7, 14, 21 and 46 days in the carbonatization chamber. The carbonatization coefficient KN was calculated as follows:

dK=A+KS.Math.t1/2

KN=a.Math.b.Math.c.Math.KS

[0104] KN=carbonatization coefficient under natural conditions with a CO.sub.2 content of 0.04% [mm/year]

[0105] a=conversion from 1 day to 1 year (365/1)1/2=19.10

[0106] b=conversion factor from 4.0 to 0.04% by volume of CO.sub.2

[0107] c=correction factor for quick carbonatization

TABLE-US-00001 CO.sub.2 absorption coefficient Material KN/[mm/year] Concrete, uncoated 12.5 (without primer) Concrete, coated 0.0 (with primer - 500 g/m.sup.2)

[0108] b) Tensile Bond Strengths with and without Primer

[0109] Direct tensile bond strengths with and without primer indicate a significantly higher strength in the case of the test specimens made of concrete 2 with primer. A prefoamed PU foam (slabstock foam) introduced on primer between two concrete plates achieves tensile bond strengths of about 0.14 N/mm.sup.2, while a PU foam foamed without primer between two concrete plates (HDI methods; high-pressure metering apparatus; pressure>120 bar) and having a density of 50 g/l attains about 0.16 N/mm.sup.2 and a PU foam foamed with primer by the HDI method attains about 0.20 N/mm.sup.2. At higher densities of the PU foam and when using a primer, rupture of the foam itself occurs, depending on the strength of the concrete.

[0110] Example I) with Primer, Concrete 2:

[0111] with PU foam having a density of 50 g/l: failure of the PU foam at 0.20 N/mm.sup.2

[0112] with PU foam having a density of 100 g/l: failure of the concrete test specimen at 0.23 N/mm.sup.2

[0113] Example II) with Primer, Concrete 3:

[0114] Concrete strength 81.9 MPa

[0115] with PU foam having a density of 90 g/l: failure of the foam at 0.32 N/mm.sup.2

[0116] c) Load/Deformation with and without High-Pressure Injection

[0117] To determine the load-bearing capability of the sandwich element having a PU foam core between plates of concrete 1, load-displacement curves were measured under a shear stress. Test specimens: cut from the sandwich elements. Dimensions 2525 cm2.5 cm concrete plates, 15 cm foam thickness. The results are shown in graph form in FIG. 2. In the case of a PU slabstock foam adhesively bonded in, sudden failure of the composite occurs: the foam delaminates from the sandwich element (broken line). All foams introduced by the HDI method display ductile failure, i.e. at the same load, greater and more uniform deformation, rather than sudden failure, occurs.

[0118] Broken line: Slabstock foam as plate having a density of 50 g/l (compaction 1.0) adhesively bonded in using PU

[0119] Building foam: max. load 15 kN and max. deformation 10 mm

[0120] Black: Injection foam having a density of 50 g/l (compaction about 1.5) with primer: max. load about 15 kN and max. deformation 20 mm

[0121] Dot-dash: Injection foam having a density of 30 g/l (compaction about 1.3) without primer: max. load about 10 kN and max. deformation>40 mm

[0122] Dots: Injection foam having a density of 50 g/l (compaction about 1.5) without primer: max. load about 10 kN and max. deformation 25 mm

[0123] d) Thermal Conductivity with and without Primer

[0124] The primers were an epoxy primer and a PU primer.

[0125] The sandwiches are produced with two concrete test specimens and rigid PU foam in the middle. The open sides are lined with vacuum packaging film in the mold.

[0126] Dimensions of concrete shells: 20202.0 cm

[0127] Foam volume between the concrete shells: 20206 cm (2.4 1)

[0128] The open sides are lined with VIP film (vacuum insulation panel) in the mold.

[0129] Plates composed of PU foam are protected against outward diffusion of cell gases by means of laminated-on aluminum foil having a thickness of 80 m (reference). Exchange of the cell gas can likewise be prevented by use of an epoxy primer (concrete system) with a thickness of 500 g/m.sup.2. The results shown are measured thermal conductivities (T.C.) after accelerated aging, i.e. storage at 60 C. for 42 days.

TABLE-US-00002 Thermal conductivity [mW/m .Math. K] PU foam with VIP film lamination 23.1 PU foam without lamination 26.7 Concrete element, not predried, 23.1 with epoxy primer 500 g/m.sup.2 Concrete element, predried, with 23.7 epoxy primer 500 g/m.sup.2 Concrete element, predried, with 26.3 PU primer 500 g/m.sup.2 Concrete element, predried, 25.5 without primer

EXAMPLE 2

Anisotropy Studies

[0130] Three test specimens were produced. A volume of 20206 cm.sup.3 (2.4 1) which was bounded by 2 cm thick concrete plates was filled with a polyurethane foam. The polyurethane foam (PU foam) used was produced on the basis of polymeric MDI and polyether polyol and formic acid, 1,1,1,3,3-pentafluorobutane and 1,1,1,3,3-penta-fluoropropane as blowing agents.

[0131] The specimen compacted, FD 45 was foamed by means of high-pressure injection foam having a compaction of about 1.35. The overall injected foam density (amount of liquid polyurethane material introduced divided by the total volume of the volume filled with foam) was about 45 kg/m3.

[0132] The specimen free, FD 45 was free-foamed by filling with poured foam. The amount of blowing agents was reduced so that an overall injected foam density of about 45 kg/m.sup.3 was attained.

[0133] The specimen free, FD 38 was free-foamed by filling with poured foam. The composition of the liquid polyurethane material corresponded to the specimen compacted, FD 45; owing to the lack of compaction, an overall injected foam density of only about 38 kg/m.sup.3 was obtained.

[0134] Square parallelepipeds of 55 cm.sup.2 and a thickness of 50 mm were cut in three directions in space from the foam bodies obtained. The mechanical properties of the test specimens in the thickness direction of the parallelepipeds was examined in accordance with DIN EN ISO 844.

[0135] The compressive strength [N/mm.sup.2] and compressive modulus were determined at 10% compression/min.

[0136] The thermal conductivity was determined in accordance with DIN EN 12667. The results are summarized in the following table (Std. dev.=standard deviation).

TABLE-US-00003 TABLE Compacted, FD45 Free, FD45 Free, FD38 Perpendicular to the Perpendicular to the Perpendicular to the covering layer (x) covering layer (x) covering layer (x) Test feature Average Std. dev. Unit Average Std. dev. Unit Average Std. dev. Unit Compressive 0.085 0.004 N/mm.sup.2 0.092 0.008 N/mm.sup.2 0.046 0.003 N/mm.sup.2 strength/stress Compression 10.0 0.0 % 7.1 2.4 % 10.0 0.1 % Compressive 2.7 0.34 N/mm.sup.2 2.82 0.40 N/mm.sup.2 1.18 0.03 N/mm.sup.2 modulus Thermal 21.8 0.0 mW/m*K 22.4 0.0 mW/m*K 21.9 0.0 mW/m*K conductivity Parallel to the rise Parallel to the rise Parallel to the rise direction (z) direction (z) direction (z) Test feature Average Std. dev. Unit Average Std. dev. Unit Average Std. dev. Unit Compressive 0.100 0.018 N/mm.sup.2 0.208 0.002 N/mm.sup.2 0.122 0.002 N/mm.sup.2 strength/stress Compression 7.9 1.8 % 4.4 0.2 % 4.3 0.3 % Compressive 2.66 0.56 N/mm.sup.2 6.99 0.06 N/mm.sup.2 3.95 0.26 N/mm.sup.2 modulus Third direction/width (y) Third direction/width (y) Third direction/width (y) Test feature Average Std. dev. Unit Average Std. dev. Unit Average Std. dev. Unit Compressive 0.093 0.014 N/mm.sup.2 0.117 0.015 N/mm.sup.2 0.102 0.005 N/mm.sup.2 strength/stress Compression 6.7 2.9 % 9.0 1.0 % 6.9 2.6 % Compressive 2.54 0.52 N/mm.sup.2 2.95 0.80 N/mm.sup.2 2.87 0.17 N/mm.sup.2 modulus
The specimen compacted, FD 45 shows low anisotropy (ratio of compressive modulus parallel to the rise direction/perpendicular to the covering layer=1.18) and a good insulation value of 21.8 mW/m*K. The specimen free, FD 45 has a comparable compressive strength perpendicular to the covering layer, but displays a poorer thermal insulation value. The specimen free, FD 38 has an unsatisfactory compressive strength perpendicular to the covering layer.