Production Of Fine Cell Foams Using A Cell Aging Inhibitor

Abstract

The use of an Ostwald hydrophobe in the production of polymer foams, preferably polyurethane foam, in particular rigid polyurethane foam, from liquid reaction mixtures, to retard cell ageing, in particular to retard cell ageing caused by Ostwald ripening, is described.

Claims

1. A method or making polymer foams from liquid reaction mixtures, to retard cell ageing, in particular to retard cell ageing caused by Ostwald ripening, said method comprising the step of a) adding from from 0.0001 to 5% by mass an Ostwald hydorphobe to a misture for the polymer foam, and b) reacting the mixture of step a) wherein the polymer foam has a standardized ageing rate k.sub.stand of 1.010.sup.3 mm.sup.2/s.

2. The method according to claim 1, wherein the standardized ageing rate k.sub.stand is 0.910.sup.3 mm.sup.2/s.

3. The method according to claim 1, wherein the total quantity of Ostwald hydrophobe is from 0.0001 to at most 3% by mass, based on the total mass of the foam formulation inclusive of the blowing agents.

4. The method according to claim 1, wherein the standardized ageing rate k.sub.stand, which can be determined as described herein, is reduced by at least 20%, when measured in comparison with the value of k.sub.stand without addition of the additional substances to retard cell ageing.

5. The method according to claim 1, wherein the Ostwald hydrophobe, under standard conditions, has a boiling point below 150 C. and low solubility in the liquid foam matrix, where this means that, when the concentration used thereof is at most 5% by mass, it leads to visible haze and/or phase separation, and in the case of foams produced via foaming of multicomponent reactive systems the said criterion preferably applies independently for all of the individual components, and in particular in the case of a polyurethane system the Ostwald hydrophobe prcfcrably has low solubility not only in the polyol mixture, corresponding to A component, but also in the isocyanate, corresponding to B component.

6. The method according claim 1, wherein the Ostwald hydrophobe is selected from the group consisting of fluorinated hydrocarbons, ethers and/or ketones in which at least 50%, of the hydrogens have been replaced by fluorine atoms, where these compounds can be saturated or unsaturated, and also linear, branched or cyclic.

7. The method according to claim 6, wherein the Ostwald hydrophobe is selected from the group consisting of perfluorinated hydrocarbons, perfluoropentane C.sub.5F.sub.12, perfluorohexane C.sub.6F.sub.14, perfluorocyclohexane C.sub.6F.sub.12, perfluoroheptane C.sub.7F.sub.16, perfluorooctane C.sub.8F.sub.18, olefins with the molecular formulae C.sub.5F.sub.10, C.sub.6F.sub.12, C.sub.7F.sub.14 and/or C.sub.8F.sub.16, dimer of 1,1,2,3,3,3-hexafluoro-1-propene, 1,1,1,2,3,4,5,5,5-nonafluoro-4-(trifluoromethyl)pent-2-ene or 1,1,1,3,4,4,5,5,5 -nonafluoro-2-(trifluoromethyl)pent-2-ene and/or mixtures thereof.

8. The method according to claim 1, wherein the Ostwald hydrophobe is selected from fluorocarbons with olefin function, C.sub.4H2F.sub.6, hexafluoroisobutylene, C.sub.5H2F.sub.8, C.sub.6H2Fio, C.sub.7H2F.sub.12 and/or C.sub.8H2F.sub.14, or olefins with the general formula
H.sub.2CCHR.sup.F where R.sup.F is a monovalent, perfluorinated, saturated organic moiety.

9. Use according to claim 1, wherein the Ostwald hydrophobe is selected from the group consisting of ethers having one or two perfluorinated moieties having the general formula
ROR.sup.F where R.sup.F is a monovalent, perfluorinated, saturated organic moiety, R is a monovalent, saturated hydrocarbon moiety, or
R.sup.FOCFCF.sub.2 where R.sup.F is a monovalent, perfluorinated, saturated organic moiety.

10. The method according to claim 1, wherein the Ostwald hydrophobe is selected from the group consisting of ketones having two perfluorinated moieties, particularly preferably 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone.

11. The method according to claim 1, wherein the Ostwald hydrophobe is selected from the group consisting of silanes and/or siloxanes which bear methyl substituents or higher hydrocarbon substituents, where these may be saturated or unsaturated, linear, branched or cyclic, and also non-halogenated, or partially or fully halogenated, in particular fluorinated, where preference is given to the following: i) tetramethylsilane and compounds of the general formula
(CH.sub.3).sub.3SiR derived therefrom, where R is H, ethyl, vinyl, allyl, chloromethyl, bromomethyl, methoxymethyl, trifluoromethyl or methoxy, ii) hexamethyldisilane, tetraethylsilane, trifluoromethyltriethylsilane and/or trivinylsilane, iii) hexamethyldisiloxane and compounds of the general formula
R(CH.sub.3).sub.2SiOSi(CH.sub.3).sub.2R derived therefrom, where R is H, ethyl, vinyl, allyl, chloromethyl, bromomethyl, methoxymethyl, trifluoromethyl or methoxy, iv) octamethyltrisiloxane and/or heptamethyltrisiloxane (CH.sub.3).sub.3SiOSi(CH.sub.3)HOSi(CH.sub.3).sub.3.

12. The method according to claim 1, wherein the polymer foam is a a rigid polyurethane foam, and results from reaction of one or more polyol components with one or more isocyanate components, in the presence of at least one urethane catalyst and/or isocyanurate catalyst, and of at least one blowing agent.

13. The method according to claim 1 wherein the polymer foam have an average cell size below 0.2 mm.

14. A polymer foam having an average cell size below 0.2 mm. produced according to claim 1.

15. A thermal insulation comprising the polymer foam according to claim 14.

16. A method or making rigid polyurethane foam from liquid reaction mixtures, to retard cell ageing, in particular to retard cell ageing caused by Ostwald ripening, said method comprising the steps of a) adding from from 0.0001 to 3% by mass an Ostwald hydorphobe to a misture for the polymer foam; and b) reacting the mixture of step a) wherein the polymer foam has a standardized ageing rate k.sub.stand of 0.810.sup.3 mm.sup.2/s.

17. The method according to claim 16, wherein the total quantity of Ostwald hydrophobe is from 0.0001 to 1.5% by mass, based on the total mass of the foam formulation inclusive of the blowing agents.

18. The method according to claim 16, wherein the standardized ageing rate kstand, which can be determined as described herein, is reduced by at least 50%, when measured in comparison with the value of k.sub.stand without addition of the additional substances to retard cell ageing.

19. The method according to claim 16, wherein the Ostwald hydrophobe, under standard conditions, has a boiling point below 150 C. and low solubility in the liquid foam matrix, where this means that, it leads to visible haze and/or phase separation, and in the case of foams produced via foaming of multicomponent reactive systems the said criterion preferably applies independently for all of the individual components, and in particular in the case of a polyurethane system the Ostwald hydrophobe has low solubility not only in the polyol mixture, corresponding to A component, but also in the isocyanate, corresponding to B component.

20. The method according to claim 6, wherein the Ostwald hydrophobe is selected from the group consisting of perfluorinated hydrocarbons, perfluoropentane C.sub.5F.sub.12, perfluorohexane C.sub.6F.sub.14, perfluorocyclohexane C.sub.6F.sub.12, perfluoroheptane C.sub.7F.sub.16, perfluorooctane C.sub.8F.sub.18, olefins with the molecular formulae C.sub.5F.sub.10, C.sub.6F.sub.12, C.sub.7F.sub.14 and/or CsF.sub.16, dimer of 1,1,2,3,3,3-hexafluoro-1-propene, 1,1,1,2,3,4,5,5,5-nonafluoro-4-(trifluoromethyl)pent-2-ene or 1,1,1,3,4,4,5,5,5-nonafluoro-2-(trifluoromethyl)pent-2-ene and/or mixtures thereof.

Description

EXAMPLES

[0072] The present invention is described by way of example in the Examples set out below.

Comparative Example 1

Production of a Rigid PU Foam Without Measures for the Avoidance of Ageing Processes Caused by Ostwald Ripening Rather Than by Coalescence

[0073] Formation of a rigid PU foam was observed by using a VHX 2000 digital microscope from Keyence, equipped with a VH-Z20R/W zoom objective. The method selected for the experiment was the transmitted-light method mentioned in the European Patent Application EP15196930.0. For this, the objective was clamped into the microscope unit with viewing direction upwards and placed below a Petri dish resting on a support ring. An optical conductor attached to the lamp housing of the microscope control unit served as illumination source. Protection was provided here by surrounding the open end of the optical conductor with a single-use screw-lid glass container with flat base, equipped with lid which had been modified to provide an appropriate passage and through which the optical conductor is passed. The illumination source thus constructed was placed at a distance of about 5 mm above the base of the Petri dish, the direction of illumination here being downwards. Care was taken here to ensure that the cone of illumination was as precisely as possible within the cone of observation of the objective. The magnification selected for observation of the foam-forming procedure was 100. The focus of the objective was adjusted to be at the base of the Petri dish.

[0074] The PU foam system used was a cyclopentane-blown rigid PU foam produced via reaction of 100 parts by weight of a polyol mixture comprising an aliphatic polyether polyol (glycerol/sorbitol-started) with OH number 470 mg KOH/g and an autocatalytic polyether polyol (o-TDA-started) with OH number 460 mg KOH/g in a mass ratio of 3:2, with 135 parts by weight of commercially available polymeric diphenylmethane diisocyanate (pMDI with viscosity 200 mPas). The polyol mixture here also comprisedbased on 100 parts by weight of the main polyol2.6 parts by weight of water, 1.5 parts by weight of the catalyst dimethylcyclohexylamine, 1.0 part by weight of the catalyst pentamethyldiethylenetriamine, 0.5 part by weight of the catalyst tris(dimethylaminopropyl)hexahydro-1,3,5-triazine, 2.0 parts by weight of the polyethersiloxane-based foam stabilizer Tegostab B 8491 from Evonik Industries AG, and also 15.0 parts by weight of cyclopentane. The reaction components were mixed in the mixing head of a high-pressure foam machine from Krauss-Maffei (RIM-Star MiniDos with MK12/18ULP-2KVV-G-80-I mixing head) at 150 bar. Directly after discharge from the mixing head, about 5 g of the reaction mixture were placed into the Petri dish of the microscopy setup and monitored videomicroscopically for 3 minutes at 100 magnification. Simply by using qualitative observation of the recorded images, it was possible to observe distinct ageing due to Ostwald ripening, i.e. the slow disappearance of small foam bubbles without coalescence. In contrast, almost no ageing phenomena due to coalescence were discernible.

[0075] Ostwald ripening during the course of the foaming process was then further examined by extracting 19 individual images from the recorded video at uniform time intervals within the observation period of from 10 to 110 sec. On the basis of the final individual image after 110 sec, four cells were then identified which were within the four corners of the image and which did not age during foaming, and which were therefore visible on all of the individual images. A rectangle representing the observation window at the respective point in time was then drawn around the said cells in all of the individual images. This procedure ensured that the growth rate of the observation window was approximately the same as that of the PU foam to be studied, thus allowing study of Ostwald ripening decoupled from the growth of the foam. The number of foam cells within the observation window at each point in time was then determined, standardized on the basis of the size of the observation window in the final individual image, and then plotted semilogarithmically as a function of time. FIG. 1 shows the result. As can be seen, the number of bubbles decreases constantly with increasing reaction time. For mathematical modelling, the data were fitted to an e function of the form N(t)=(N.sub.0N.sub.u)e.sup.kt+N.sub.u. This gave a standardized initial bubble number N.sub.0=1626.7 mm.sup.2, an ageing rate k=0.120 s.sup.1 and a standardized bubble number N.sub.u=103.2 mm.sup.2 for the hardened foam. From these values it is possible to determine a standardized ageing rate k.sub.norm=1.1610.sup.3 mm.sup.2/s.

Inventive Example 2

Production of a Rigid PU Foam Comprising Ostwald Hydrophobe

[0076] These experiments used the reaction system described in Comparative Example 1, to which 2 parts by weight of perfluoroisohexene were added. For this, the perfluoroisohexene was first mixed with cyclopentane; this mixture was then added as described in Example 1 to the polyol phase of the reaction system. The system was foamed and observed videomicroscopically by analogy with Example 1. Simply from qualitative examination of the recorded images, it was possible to discern significant retardation of ageing processes when comparison is made with the perfluoroisohexene-free PU system. The curve for standardized cell number N(t) as a function of time was then determined from the recorded videomicroscopic images as described in Example 1. FIG. 2 shows the result. By mathematical modelling of the data using the general expression N(t)=(N.sub.0N.sub.u)e.sup.kt+N.sub.u, it was possible to determine a standardized initial bubble number N.sub.0=1473.4 mm.sup.2, an ageing rate k=0.162 s.sup.1 and a standardized bubble number N.sub.u=295.4 mm.sup.2 for the hardened foam. This gives a standardized ageing rate k.sub.stand=5.4810.sup.4 mm.sup.2/s. When comparison is made with the perfluoroisohexene-free PU system from Example 1, therefore, a marked decrease of the standardized ageing rate k.sub.stand can be discerned; this is attributable to retarded cell ageing. Microscopic examination of the finished foam moreover revealed that the reduced cell-ageing rate caused a significant reduction in the average size of the foam cells. It was below 0.2 mm.