Polyurethane foam and method for producing same

Abstract

The invention relates to a method for producing a polyurethane foam, wherein a mixture having the following is discharged from a mixing head through a discharge line: A) a component reactive toward isocyanates; B) a surfactant component; C) a blowing agent component selected from the group comprising linear, branched, or cyclic C1 to C6 hydrocarbons, linear, branched, or cyclic C1 to C6 fluorocarbons, N2, O2, argon, and/or CO2, wherein the blowing agent C) is present in the supercritical or near-critical state; and D) a polyisocyanate component. The component A) has a hydroxyl value=100 mg KOH/g and =1000 mg KOH/g. The blowing agent component C) is present at least partially in the form of an emulsion, and means provided with an opening or several openings are arranged in the discharge line in order to increase the flow resistance during the discharge of the mixture comprising A), B), C), and D), wherein the cross-sectional area of the opening or the sum of the cross-sectional areas of all openings is =0.1% and =99.9% of the inner cross-sectional area of the discharge line.

Claims

1. A method of producing a polyurethane foam comprising the steps of: providing a mixture in a high-pressure mixing head, said mixture comprising: A) an isocyanate-reactive component; B) a surfactant component; C) a blowing agent component selected from the group consisting of a linear C.sub.1 to C.sub.6 hydrocarbon, a branched C.sub.1 to C.sub.6 hydrocarbon, a cyclic C.sub.1 to C.sub.6 hydrocarbon, a linear C.sub.1 to C.sub.6 fluorocarbon, a linear C.sub.1 to C.sub.6 hydrofluorocarbon, a branched C.sub.1 to C.sub.6 fluorocarbon, a branched C.sub.1 to C.sub.6 hydrofluorocarbon, a cyclic C.sub.1 to C.sub.6 fluorocarbon, a cyclic C.sub.1 to C.sub.6 hydrofluorocarbon, N.sub.2, O.sub.2, argon, and CO.sub.2, wherein said blowing agent C) is in the supercritical or near-critical state; and D) a polyisocyanate component; discharging the mixture comprising A), B), C) and D) from the mixing head through a discharge line, wherein a pressure of ≧80 bar to ≦150 bar prevails in the mixing head after the step of providing the mixture, wherein said isocyanate-reactive component A) has a hydroxyl number of ≧100 mg KOH/g to ≦1000 mg KOH/g, said blowing agent component C) is at least partly present in the form of an emulsion, wherein the proportion of blowing agent component C) is ≧4% to ≦40% by weight based on the overall weight of the mixture, and one or more apertures are disposed in the discharge line to elevate the flow resistance during the step of discharging the mixture comprising A), B), C) and D), wherein the one or more apertures comprises a cross-sectional area, wherein the cross-sectional area of the one or more apertures or the sum total of a single cross-sectional area of each of said one or more apertures amounts to ≧0.1% to ≦99.9% of the inner cross-sectional area of the discharge line.

2. The method as claimed in claim 1 wherein the cross-sectional area of the one or more apertures or the sum total of a single cross-sectional area of each of said one or more apertures amounts to ≧0.5% to ≦10% of the inner cross-sectional area of the discharge line.

3. The method as claimed in claim 1 wherein the ratio of the volume of a reaction chamber which is inside and/or outside the mixing head to the cross-sectional area of the one or more apertures or to the sum total of the cross- sectional areas of all apertures is ≧5 m to ≦200 m.

4. The method as claimed in claim 1 wherein the step of discharging the mixture comprising A), B), C) and D) from the mixing head is effected such that the ratio of the volume flow of the mixture to the cross-sectional area of the one or more apertures or to the sum total of the cross-sectional areas is >5 m/s to <400 m/s.

5. The method as claimed in claim 1 wherein the mixture in the mixing head has a residence time ≧0 seconds to ≦20 seconds.

6. The method as claimed in claim 1 wherein said isocyanate-reactive component A) comprises a polyetherester polyol having a hydroxyl number of ≧200 mg KOH/g to ≦600 mg KOH/g and a short-chain polyol having a hydroxyl number of ≧800 mg KOH/g.

7. The method as claimed in claim 1 wherein said surfactant component B) comprises a polysiloxane-polyoxyalkylene copolymer.

8. The method as claimed in claim 1 wherein the proportion of blowing agent component C) is ≧4% by weight to ≦12% by weight, based on the overall weight of the mixture.

9. The method as claimed in claim 1 wherein said polyisocyanate component D) comprises monomeric and/or polymeric diphenylmethane 4,4′-diisocyanate.

10. A polyurethane foam obtained by the method of claim 1.

11. The polyurethane foam as claimed in claim 10 with an apparent density of ≧20 kg/m.sup.3 to ≦160 kg/m.sup.3.

12. The method as claimed in claim 1, wherein said isocyanate-reactive component A) comprises a polyetherester polyol having a hydroxyl number of ≧200 mg KOH/g to ≦600 mg KOH/g and a short-chain polyol having a hydroxyl number of ≧800 mg KOH/g, and wherein the polyurethane foam has an apparent density of 30 kg/m.sup.3 to ≦120 kg/m.sup.3.

13. The method as claimed in claim 12, wherein the proportion of blowing agent component C) is >7% by weight to <9% by weight, based on the overall weight of the mixture.

14. The method as claimed in claim 1 wherein the mixture in the mixing head has a residence time ≧0.5 seconds to ≦5 seconds.

Description

(1) Preferred embodiments of the method according to the present invention will now be more particularly described. They can be combined in any desired manner unless the contrary is apparent from the context.

(2) In one embodiment, the cross-sectional area of the aperture or the sum total of the cross-sectional areas of all apertures amounts to ≧0.5% to ≦10% of the inner cross-sectional area of the discharge line. One aperture is preferably in the form of an outlet nozzle. Preferred ranges for the cross-sectional area of the aperture or the sum total of the cross-sectional areas of all apertures are ≧0.7% to ≦2.5%.

(3) In a further embodiment, the ratio of the volume of a reaction chamber which is inside and/or outside the mixing head and in which supercritical conditions prevail, to the cross-sectional area of the aperture or to the sum total of the cross-sectional areas of all apertures is ≧5 m to ≦200 m.

(4) The reaction chamber can be formed within the mixing head by the mixing chamber thereof. Outside the mixing head, the reaction chamber can be formed by that part of the discharge line which is upstream of the means for elevating the flow resistance in the step of discharging the mixture comprising A), B), C) and D). In the simplest case, therefore, the volume of the discharge line upstream of a perforate plate contributes to the volume of the reaction chamber.

(5) The recited ratios provide optimum control over the flow of the mixture as a result of viscosity increase during the PU reaction. Preferred ratios are ≧10 m to ≦100 m.

(6) In a further embodiment, the step of discharging the mixture comprising A), B), C) and D) from the flow resistance elevator means having one or more apertures is effected such that the ratio of the volume flow of the discharged mixture to the cross-sectional area of the aperture or to the sum total of the cross-sectional areas is ≧5 m/s to ≦400 m/s.

(7) Again, the recited ratios provide optimum control over the flow of the mixture as a result of viscosity increase during the PU reaction. Preferred ratios are ≧40 m/s to ≦200 m/s.

(8) In a further embodiment, a pressure of ≦40 bar to ≧150 bar prevails in the mixing head after the step of providing the mixture. This state can prevail particularly in a mixing head and downstream of a mixing head. The pressure can also be ≧80 bar to ≦120 bar or ≧60 bar to ≦100 bar. Pressures of this type will maintain supercritical or near-critical conditions for the blowing agent used.

(9) In a further embodiment, the mixture in the mixing head has a residence time ≧0 seconds to ≦20 seconds, preferably ≧0.1 second to ≦10 seconds and more preferably ≧0.5 second, to ≦5 seconds under supercritical or near-critical conditions of the blowing agent. This ensures that the mixture can polymerize under supercritical or near-critical conditions. The residence time can be determined by the volume of the reaction chamber (=total volume of mixing chamber with efflux pipe up to the perforate plate) in which supercritical or near-critical conditions prevail, divided by the volume of mixture conveyed per unit time.

(10) In a further embodiment, said isocyanate-reactive component A) comprises a polyetherester polyol having a hydroxyl number of ≧200 mg KOH/g to ≦600 mg KOH/g and a short-chain polyol having a hydroxyl number of ≧800 mg KOH/g. Suitable polyetherester polyols include bifunctional polyetherester polyol which are obtained by addition of alkylene oxides and especially ethylene oxide onto a mixture of phthalic anhydride, diethylene glycol and ethylenediamine and have an OH number of ≧275 mg KOH/g to ≦325 mg KOH/g.

(11) Products of this type are available from Bayer MaterialScience AG under the trade name of Desmophen® VP.PU 1431. The OH number of the polyester polyol can also be ≧290 mg KOH/g to ≦320 mg KOH/g. Short-chain polyols are polyols having ≧2 to ≦6 carbon atoms in particular. Glycerol is preferred. It has an OH number of 1827 mg KOH/g. Adding the short-chain polyol is a favorable way to increase the polarity of the polyol phase.

(12) In a further embodiment, surfactant component B) comprises a polysiloxane-polyoxyalkylene copolymer. The polysiloxane-polyoxyalkylene copolymer (silicone-glycol copolymer) preferably concerns compounds registered under CAS number 87244-72-2.

(13) In a further embodiment, the proportion of blowing agent component C) is ≧4% by weight to ≦12% by weight, based on the overall weight of the mixture. Preferred proportions are ≧6% by weight to ≦10% by weight and particularly preferred proportions are ≧7% by weight to ≦9% by weight.

(14) In a further embodiment, said polyisocyanate component D) comprises monomeric and/or polymeric diphenylmethane 4,4′-diisocyanate. A polyisocyanate of this type is available from Bayer MaterialScience under the trade name of Desmodur® 44V70L as a mixture of diphenylmethane 4,4′-diisocyanate (MDI) with isomers and higher-functional homologs.

(15) The present invention further provides a polyurethane foam obtained or obtainable by a method of the present invention.

(16) In one embodiment, the polyurethane foam has an apparent density of ≧20 kg/m.sup.3 to ≦160 kg/m.sup.3. Apparent density can be determined according to DIN EN 1602 and is preferably ≧30 kg/m.sup.3 to ≦120 kg/m.sup.3 and more preferably ≧40 kg/m.sup.3 to ≦80 kg/m.sup.3. Thermal insulation is among preferred uses for the foam of the present invention.

(17) The examples which follow are offered by way of elucidation, not limitation, of the present invention.

(18) Glossary:

(19) Desmophen® VP.PU 1431: bifunctional polyetherester polyol, EO adduct onto a mixture of phthalic anhydride, diethylene glycol and ethylenediamine, with an OH number of 275 to 325 mg KOH/g and a viscosity of 6.5±1.3 Pa s at 25° C.; Bayer MaterialScience AG. DABCO® DC198: product from Air Products; stabilizer/surfactant. DABCO® DC198 is a polysiloxane-polyoxyalkylene copolymer (silicone-glycol copolymer). Compounds of this type are registered under CAS number 87244-72-2. DBTL: dibutyltin dilaurate. Desmorapid® 726b: catalyst from Bayer MaterialScience AG. Desmodur® 44V70L: mixture of diphenylmethane 4,4′-diisocyanate (MDI) with isomers and higher-functionality homologs from Bayer MaterialScience AG.

EXAMPLE 1 TO EXAMPLE 4 AND ALSO COMPARATIVE EXAMPLES COMPARATOR 1 AND COMPARATOR 2

(20) CO.sub.2-blown polyurethane foams were produced in accordance with the recipes recited below in Table 1. Unless otherwise stated, quantities are given in parts by weight. The mixture of isocyanate-reactive compound A) was mixed with added components such as surfactants B) and catalysts. It was used as the polyol component in a standard high-pressure mixing rig and mixed with blowing agent C) at a pressure of 120 bar. Supercritical conditions prevailed for the blowing agent during the mixing. This mixture was mixed in a high-pressure mixing head with a polyisocyanate D), which was conveyed at a pressure of 120 bar. The blowing agent was at least partly present in the form of an emulsion under the conditions prevailing in the mixing head.

(21) Shot quantity was 60 g/s, corresponding to a volume stream of 72 ml/s (density of mixture 1.2 g/ml). The efflux pipe of the mixing head had an inner diameter of 8.5 mm and a length of about 50 cm. The total volume of the mixing chamber including the efflux pipe up to the perforate plate was 36 ml. A perforate plate having the hole size specified in the tables was fitted in the efflux pipe downstream of the mixing head in the inventive examples. This made it possible to set the pressure in the mixing head in a controlled manner and achieve a slower reduction in the pressure in the reaction mixture.

(22) Comparative Examples 1 and 2, which were deliberately set to a low pressure in contrast to Examples 1 to 4, have a distinctly higher apparent density. This shows that distinctly worse use was made here of the blowing agent.

(23) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Comparator 1 Comparator 2 Desmophen ® 95.00 95.00 95.00 95.00 95.00 95.00 VP.PU 1431 glycerol 15.00 15.00 15.00 15.00 15.00 15.00 DABCO ® DC198 2.00 2.00 2.00 2.00 2.00 2.00 DBTDL 0.06 0.06 0.06 0.06 0.06 0.06 Desmorapid ® 0.30 0.30 0.30 0.30 0.30 0.30 726b CO.sub.2 27.50 27.50 28.60 28.60 28.60 27.50 Desmodur ® 137.89 137.89 151.67 151.67 151.67 137.89 44V70L index 100.00 100.00 110.00 110.00 110.00 100.00 isocyanate 36 35 35 35 35 34 temperature [° C.] polyol 35 34 34 34 34 34 temperature [° C.] OH number of 517 517 517 517 517 517 component A) [mg KOH/g] shot time [s] 10 10 10 10 10 10 counterpressure 95-87 92-78 81-75 50-40 2.6-2 2.8-2.1 [bar] perforate plate 0.8 1.2 0.8 1.2 absent absent [mm] pipe diameter 8.5 8.5 8.5 8.5 8.5 8.5 [mm] residence time of 0.5 0.5 0.5 0.5 none none mixture under super- or near- critical conditions [s] free-rise density 94 101 113 90 238 223 of core [kg/m.sup.3]