Process for producing composite profiles

Abstract

The present invention relates to a process for producing composite profiles comprising at least two metal shells which are joined by struts comprising a thermoplastic material and a core comprising rigid polyurethane foam, which comprises introduction of the starting components of the rigid polyurethane foam into a hollow space formed by the metal shells, with the rigid polyurethane foam being formed, and subsequent application of a surface coating to the outer surface of the composite profile by means of a powder coating or baking enamel, where the rigid polyurethane foam is obtained by reaction of the following components: A) at least one polyisocyanate, B) at least one polyfunctional compound which is reactive toward isocyanates, C) one or more blowing agents comprising at least formic acid, D) optionally one or more flame retardants, E) optionally one or more catalysts and F) optionally further auxiliaries or additives,
wherein the starting components of the rigid polyurethane foam do not comprise any inorganic fillers.

Claims

1. A process for producing a composite profile, comprising: introducing starting components of rigid polyurethane foam into a hollow space formed by at least two metal shells to obtain the rigid polyurethane foam, and subsequently applying a surface coating to an outer surface of the composite profile by powder coating or baking enamel, wherein: the composite profile comprises the at least two metal shells joined by struts, the struts comprise a thermoplastic material and a core comprising the rigid polyurethane foam, and the starting components of the rigid polyurethane foam comprise: A) a polyisocyanate, B) a polyfunctional compound which is reactive toward isocyanates, C) a blowing agent comprising at least formic acid, D) optionally a flame retardant, E) optionally a catalyst, F) optionally further auxiliaries or additives, and no inorganic fillers.

2. The process according to claim 1, wherein component C) is an aqueous solution of formic acid.

3. The process according to claim 2, wherein component C) is a solution of from 70 to 95% by weight of formic acid in water.

4. The process according to claim 1, wherein an amount of formic acid based on a total weight of components B) to F) is from 2 to 6% by weight.

5. The process according to claim 1, wherein component B) comprises exclusively compounds which are obtained by alkoxylation of a starter by exclusively propylene oxide.

6. The process according to claim 1, wherein component B) comprises a polyether polyol having a hydroxyl number of from 200 to 400 mg KOH/g and a functionality of from 2 to 3.

7. The process according to claim 1, wherein component B) comprises a polyether polyol having a hydroxyl number of from 300 to 600 mg KOH/g and a functionality of from 4 to 8.

8. The process according to claim 1, wherein a weight average functionality of component B) is from 2.4 to 5.

9. The process according to claim 1, wherein the surface coating is applied at a temperature of from 100 to 250° C.

10. The process according to claim 1, wherein the starting components of the rigid polyurethane foam comprise: A) a polyisocyanate, B) a polyfunctional compound which is reactive toward isocyanates, C) a blowing agent comprising at least formic acid, D) a flame retardant, E) a catalyst, F) optionally further auxiliaries or additives, and no inorganic fillers.

Description

(1) The invention is illustrated by the following examples.

(2) The following polyols were used:

(3) Polyol B-1: polyether polyol having a hydroxyl number of 490 mg KOH/g and based on propylene oxide and sorbitol as starter

(4) Polyol B-2: polyether polyol having a hydroxyl number of 248 mg KOH/g and based on propylene oxide and propylene glycol as starter

(5) Component C-1: formic acid 85%

(6) Component C-2: water

(7) Compound D-1: tris(2-chloroisopropyl)phosphate

(8) Compound E-1: N,N-dimethylcyclohexylamine

(9) Compound F-1: silicone-based stabilizer, Niax Silicone L-6900

(10) The components shown in table 1 were mixed to form a polyol component.

(11) TABLE-US-00001 TABLE 1 Example 1 Example 2 Component Amount used [% by weight] B-1 37.1 36.5 B-2 36.5 38.5 C-1 4.5 — C-2 — 3.7 D-1 19.0 19.0 F-1 1.7 1.7 E-1 1.2 0.6

(12) A mixture of diphenylmethane 2,4′- and 4,4′-diisocyanate with higher-functional oligomers and isomers (crude MDI) having an NCO content of 31.5% (IsoPMDI 92410 from BASF) was used as isocyanate component. The foaming experiments on the laboratory scale were carried out at an isocyanate index of 115.

(13) In production experiments, polyol and isocyanate components were reacted in a low-pressure plant at an isocyanate index of 115 and used to fill aluminum-polyamide composite profiles having a height of 70 mm and a width of 250 mm with foam. These profiles were then subsequently subjected to powder coating.

(14) Furthermore, aluminum-polyamide composite profiles having a height of 3 cm and a width of 6 cm were manufactured using the rigid polyurethane foams described and subjected to powder coating at 200° C.

(15) In the case of example 1, the profile displayed no deformation even after surface coating.

(16) In contrast, when aluminum-polyamide composite profiles were filled with various filler-free foam formulations using water as blowing agent, both on the laboratory scale and on the production scale, deformation of the completely foam-filled composite elements was observed, especially as a result of surface coating (example 2).

(17) Furthermore, formulations comprising formic acid as blowing agent and comprising increasing amounts of calcium carbonate (calcium carbonate content of 0-50% by weight) were tested in laboratory and production experiments. Here, the incorporation of finely divided fillers into the reaction mixture placed severe demands on the wear resistance of the metering pumps. The corresponding formulations were tested with increasing low-temperature flexibility. Furthermore, the undesirable increase in dust after cutting or sawing of completely foam-filled hollow chamber profiles was in many cases observed in the manufacturing process. In addition, the increase in density of the finished filler-comprising polyurethane foam is disadvantageous in many cases.