Patent Application
20140213679
The invention relates to stable emulsions for the production of foams based on isocyanates, comprising at least three polyols A1a, A1b and A1c and at least one physical blowing agent T, wherein A1a is a polyether polyol, obtained by the addition of epoxies to starter compounds selected from carbohydrates and difunctional or higher-functional alcohols, A1b is a polyether polyol started on an aromatic amine and A1c is a polyester polyether polyol, obtained by the addition of epoxies to the esterification product of an aromatic dicarboxylic acid derivative and a difunctional or higher-functional alcohol. The invention further relates to a method for producing foams by reactions of such emulsions with isocyanates and to the foams obtainable in this way and their use for insulating purposes.
It is known that in the production of foams from an isocyanate component and an isocyanate-reactive component containing polyol(s) using a physical blowing agent, it has a positive influence on the insulating effect of the foam to be produced if the physical blowing agent is emulsified in the isocyanate-reactive composition in the form of fine droplets. This positive influence on the insulating effect of the foam to be produced is caused by the fact that the droplets of emulsion that are formed act as nucleating agents for the subsequent foaming process. The more droplets that exist and the finer these droplets are, the more cells there are in the subsequent foam and above all the smaller the cells are. This fact has a direct influence on the insulating properties of the foam obtained in this way, since the smaller the foam cells that are formed, the better these properties are. Good insulating properties are reflected in a low thermal conductivity. The difficulty with the manufacture and processing of such emulsions is their stability, however. This stability is defined by the non-separation of polyol formulation and physical blowing agent on simple storage of such an emulsion under normal conditions with no additional external loading over a period of several hours to days, through to loading via temperature influences and increased pressure and influences of shear forces. Only emulsions that offer precisely this stability at least under normal conditions but preferably also under conditions involving temperature change, pressure changes and/or shear forces are thus of relevance in industry. These maturing processes are generally counteracted by means of a dramatic increase in viscosity up to a doubling of the viscosity of the liquid polyol phase. Since however the processing of emulsions is in any case made more difficult by their non-Newtonian behaviour, excessive rises in viscosity are undesirable.
EP 0 905 160 A1 describes stable emulsions containing blowing agent and incorporating polyether alcohols having a functionality greater than 1.5 and a hydroxyl value of 10 to 100 mg KOH/g as reactive emulsion stabilisers (see paragraph [0014]) in the polyol component for producing rigid foams based on isocyanates (see paragraph [0001]). The emulsions contain polyether alcohols, which are produced by the addition of low alkylene oxides, preferably ethylene oxide and/or propylene oxide, to OH- and/or NH-functional starter substances, for example sugar alcohols and aromatic amines (see paragraph [0025]). Polyester alcohols produced from polyfunctional carboxylic acids and polyfunctional alcohols are preferably also added to the polyether alcohols (see paragraph [0026]). The blowing agent is emulsified in the polyol mixture and a stable emulsion is obtained (see paragraph [0021]). The blowing agent can however also be added to the polyol mixture in or just in front of the mixing head. The specific combination of the three polyols A1a, A1b and A1c mentioned in the introduction is however not disclosed in this document. In particular, no polyester polyether polyols are disclosed.
US 2002/0169228 A1 claims a phase-stable polyol mixture comprising a propylene oxide-polyether polyol co-started with sucrose and dipropylene, a polyester polyol and a hydrocarbon having 4 to 6 carbon atoms as blowing agent, which is phase-stable for at least 24 hours (cf. claim 1). A polypropylene oxide-polyether polyol having an OH functionality of between 3.5 and 4.5 started with toluene diamine can additionally also be added to the mixture (see paragraph [0020]). The polyester polyol is started with phthalic anhydride (cf. claim 3) and is preferably STEPANPOL 2352, which is based on phthalic anhydride and diethylene glycol (see paragraph [0022]). Cyclopentane can be used as the blowing agent (see paragraph [0029]), which is either present in the polyol mixture in the form of a microemulsion (see paragraph [0006]), is added to the polyol mixture just in front of the mixing head or is fed to the mixing head as a separate stream (see paragraph [0027]). The polyol mixture is reacted with an organic polyisocyanate to form a polyurethane foam (cf. claim 17). The term “microemulsion” within the meaning of this application implies that the blowing agent is dissolved in the polyol mixture; see paragraph [0006]. This also becomes clear in paragraph [0013], where it is disclosed that the polyol mixture is no longer classed as phase-stable if it has a “cloudy appearance”. The statement that the polyol composition has to remain phase-stable for at least 24 hours (see paragraph [0006]) suggests that the term “microemulsion” is used erroneously in this application. A true microemulsion is in the state of a thermodynamic minimum and is thus stable indefinitely, provided that the composition and temperature do not change. Unlike such microemulsions, emulsions are above all temperature-sensitive but also substance-sensitive. Heating and then subsequently cooling them to the starting temperature generally leads to an irreversible change in the disperse structure, which can cause the emulsion to break. Therefore maintaining the stability of a “true” emulsion as in the present invention is considerably more difficult than in the case of “microemulsions”.
The application US 2002/0169228 A1 refers consistently to the solution of the blowing agent in the polyol mixture. According to this document all factors adversely affecting the solubility of the blowing agent should be avoided, which is why only propylene oxide is used in the production of the polyether polyols (see paragraph [0018]).
WO 00/24813 A1 describes the production of rigid polyurethane foams for the thermal insulation of refrigerators, for example (page 1, lines 3 to 5). The foams consist of organic polyisocyanates, a polyol mixture comprising polyether and/or polyester polyols, a blowing agent and further auxiliary agents and additives (cf. claim 1). The blowing agent consisting of cyclopentane and water is dispersed in the polyol mixture (cf. claim 1). The polyether polyols are produced by addition polymerisation of a polyhydroxyl alcohol with polyethylene oxide and/or propylene oxide (page 4, lines 11 to 15) and preferably have 3 to 6 OH groups (page 5, lines 13 to 15). Glycerol, sorbitol, sucrose and aromatic amines for example can be used as polyhydroxyl alcohols (page 5, lines 1 to 3 and 6 to 7). The polyester polyol can be produced from dicarboxylic anhydrides (e.g. phthalic anhydride) and diols (e.g. diethylene glycol) (page 5, lines 16 to 31) and preferably has two functional groups (page 6, lines 4 to 6). Polyether polyols started on aromatic amines are disclosed in this document in the comparative examples (“polyol K”). In these comparative examples pentane is dissolved and not emulsified in the polyol component (cf. Table 1 on p. 13). The content of polyol K is relatively high, at 40% (comparative example 1) and 50% (comparative example 2) respectively, relative to all polyols present.
None of the aforementioned prior art documents discloses an isocyanate-reactive composition, in which a physical blowing agent T is dispersed in a mixture comprising the polyols A1a, A1b and A1c mentioned in the introduction such that a stable emulsion (to be distinguished from both a solution and a microemulsion) is obtained, and without the viscosity of the isocyanate-reactive composition being increased too greatly in comparison with common, completely dissolved isocyanate-reactive compositions.
Taking account of the information set out above, the present invention provides an emulsion comprising
The use of the word “a” in conjunction with components according to the invention such as for example certain polyols shall not be understood within the meaning of this application as a numerical value. Expressions such as “a polyol” or similar thus only mean “precisely one (=1) polyol” if that is expressly stated. It is conceivable for example for there to be two polyols of the type A1a.
An “emulsion” within the context of the present invention is understood to be a finely divided mixture of two liquids, in which one liquid (namely the physical blowing agent T) is dispersed in the other liquid (namely the polyol mixture A1) in the form of fine droplets showing an average size ≧0.1 μm to ≦20 μm, the droplet size being determined by using an optical microscope operating in bright field transmission mode. Such an emulsion is different from both a true solution and a microemulsion. Microemulsions have such a finely divided disperse phase that light is no longer refracted. Such microemulsions therefore appear clear and transparent in the visible light range, whereas emulsions within the meaning of the present invention appear cloudy and exhibit strong light refraction. Moreover, microemulsions can be produced only with the aid of emulsifying aids, whereas although the use of emulsifying aids in the production of the emulsions according to the invention is not excluded in principle, it is not absolutely necessary and is therefore not preferred. According to this invention, the droplet size of the blowing agent T is preferably ≧0.1 μm to ≦15 μm and more preferred ≧1 μm to ≦15 μm. The size is determined via an optical microscope using bright field transmission microscopy. Suitable layer thicknesses for the optical inspection of the specimen are 20 μm to 40 μm.
“Physical blowing agents” within the context of the present invention are understood to be compounds that by virtue of their physical properties are highly volatile and do not react with the isocyanate component.
The “hydroxyl value” indicates the amount of potassium hydroxide in milligrams that is equivalent to the amount of acetic acid bound by the acetylation of one gram of substance. In the context of the present invention it is determined in accordance with the standard DIN 53240 in the December 1971 version.
“Functionality” within the context of the present invention refers to the theoretical functionality calculated from the known substances used and the proportions thereof.
The present invention also provides a method for producing a polyurethane-containing polymer C, in which an isocyanate component B is reacted with an emulsion according to the invention.
A “polyurethane-containing polymer C” is understood here to denote both polymers containing exclusively polyurethane groups (PUR groups) and polymers that additionally contain urea and/or polyisocyanurate groups (PIR groups).
The present invention also provides the polyurethane polymers C obtainable in this way and their use for insulating purposes.
Surprisingly it has been found that through the combination according to the invention of polyols A1a, A1b and A1c, the total viscosity of the isocyanate-reactive composition and hence also the total viscosity of the emulsion can be lowered in comparison to isocyanate-reactive compositions (polyol mixtures) of the prior art that form a solution with the physical blowing agent. It has moreover been found that the stability of the emulsions according to the invention can be increased markedly by the optimisation of certain parameters (such as the content of oxyethylene groups in the polyols used). Furthermore, the thermal conductivity values achieved can be improved through the right combination of optimised polyol emulsions with suitable NCO-terminated prepolymers.
These and other findings are described below by reference to various embodiments and examples of the present invention, wherein the individual embodiments can be freely combined with one another provided that the converse is not clearly indicated from the context.
The production of the polyols A1a to A1c that can be used according to the invention (and optionally of further polyols, see below) is known in principle to the person skilled in the art and has already been described many times. Polyester polyols are obtained by polycondensation of dicarboxylic acid equivalents and low-molecular-weight polyols. Polyether polyols are obtained by polyaddition (anionic or cationic) of epoxies to suitable starter compounds. The addition of epoxies to polyester polyols leads to the polyester polyether polyols according to the invention. The polymerisation reactions are performed if necessary in the presence of suitable catalysts known to the person skilled in the art.
In preferred embodiments the polyether polyol A1a is started on sucrose, mixtures of sucrose and propylene glycol, mixtures of sucrose and ethylene glycol, mixtures of sucrose, propylene glycol and ethylene glycol, sorbitol or mixtures of sorbitol and glycerol. Preferred epoxies are 1,2-butylene oxide, 2,3-butylene oxide, ethylene oxide and propylene oxide, individually or in mixtures. Ethylene oxide and propylene oxide, which can be used individually or both together, are particularly preferred, wherein in the latter case both a random distribution of the oxyalkylene units derived from the ethylene oxide and propylene oxide and a selective production of block copolymers of a specific structure are conceivable. Mixtures of sucrose, propylene glycol and ethylene glycol are particularly preferred as the starter. Exclusively propylene oxide is particularly preferably used as the epoxy. The hydroxyl value of A1a is particularly preferably 100 mg KOH/g to 450 mg KOH/g and the functionality 2.5 to 5.
In preferred embodiments the polyether polyol A1b is started on ortho-, meta- or para-toluoylene diamine or a mixture of isomeric toluoylene diamines. ortho-Toluylene diamine is particularly preferably used as the starter. This can be in the form of a mixture of 2,3- and 3,4-isomers. In principle, however, the use of other aromatic amines is also conceivable, such as for example benzene diamine (all isomers) or methylene diphenyl diamine (all isomers). Preferred epoxies are 1,2-butylene oxide, 2,3-butylene oxide, ethylene oxide and propylene oxide, individually or in mixtures. Ethylene oxide and propylene oxide, which can be used individually or both together, are particularly preferred, wherein in the latter case both a random distribution of the oxyalkylene units derived from the ethylene oxide and propylene oxide and a selective production of block copolymers of a specific structure are conceivable. Propylene oxide is particularly preferably used, either alone or in a mixture with ethylene oxide. In the latter case the ratio by mass of propylene oxide to ethylene oxide is 0.25:1 to 4:1, most particularly preferably 0.5:1 to 2:1. In the case of block copolymers they are preferably terminated with propylene oxide.
In preferred embodiments the aromatic dicarboxylic acid derivative used in the production of the polyol A1c is a phthalic acid derivative, particularly preferably phthalic anhydride.
Preferred difunctional or higher-functional alcohols used in the production of the polyol A1c are ethylene glycol and diethylene glycol including higher homologues thereof, 1,2-propanediol, dipropylene glycol and higher homologues thereof, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol including higher homologues thereof, 2-methyl propanediol-1,3, neopentyl glycol, 3-methyl pentanediol-1,5, glycerol, pentaerythritol, 1,1,1-trimethylolpropane and carbohydrates having 5 to 12 carbon atoms (such as isosorbide for example). Ethylene glycol and diethylene glycol are most particularly preferred.
Epoxies preferably used in the production of the polyol A1c are ethylene oxide and propylene oxide. These are used in an amount such that the content of oxyethylene groups is 5 mass % to 50 mass %, preferably 10 mass % to 40 mass %, particularly preferably 15 mass % to 30 mass %, relative to the total mass of the polyol A1c.
In certain embodiments the polyol mixture A1 can also contain further polyols. Thus (iv) a short-chain polyether polyol A1d started on an aliphatic amine or a polyhydric alcohol and having a hydroxyl value from 500 mg KOH/g to 1000 mg KOH/g, preferably from 600 mg KOH/g to 950 mg KOH/g, particularly preferably from 700 mg KOH/g to 900 mg KOH/g and a functionality from 1.5 to 5.0, preferably from 2.0 to 4.5, particularly preferably from 2.5 to 4.0, can also be present. A1d is particularly preferably obtained from the addition of epoxies to ethylene diamine or trimethylolpropane. Preferred epoxies are ethylene oxide and propylene oxide, with propylene oxide being particularly preferred.
The polyol mixture A1 can furthermore also contain (v) a difunctional to tetrafunctional amine-type or alcoholic chain extender or crosslinker A1e. A1e is preferably selected from glycerol, butanediol, ethylene glycol, diethylene glycol, propylene glycol, ethylene diamine, ethanolamine, triethanolamine, trimethylolpropane and pentaerythritol.
Polyether carbonate polyols A1f, such as can be obtained for example by catalytic reaction of epoxies and carbon dioxide in the presence of H-functional starter substances (see for example EP 2 046 861 A1), can additionally also be used in the polyol mixture A1. These polyether carbonate polyols generally have a functionality of greater than or equal to 1.0, preferably from 2.0 to 8.0, particularly preferably from 2.0 to 7.0 and most particularly preferably from 2.0 to 6.0. The number-average molar mass is preferably 400 g/mol to 10,000 g/mol and particularly preferably 500 g/mol to 6000 g/mol.
Within the context of this invention the number-average molar mass Mn is determined by gel permeation chromatography in accordance with DIN 55672-1 from August 2007.
The physical blowing agent T is subject to no restrictions in principle, provided that it is not soluble in the polyol mixture A1 under the prevailing boundary conditions (temperature, pressure) (since an emulsion could not then be produced). The physical blowing agents for use according to the invention are preferably selected from hydrocarbons (e.g. n-pentane, isopentane, cyclopentane, butane, isobutane), ethers (e.g. methylal), halogenated ethers, perfluorinated hydrocarbons having 1 to 8 carbon atoms (e.g. perfluorohexane) and mixtures thereof with one another. In particularly preferred embodiments a pentane isomer or a mixture of various pentane isomers is used as the physical blowing agent T. Cyclopentane is exceptionally particularly preferably used as the blowing agent T.
In particularly preferred embodiments the emulsion according to the invention contains precisely one each of polyols A1a, A1b and A1c and, if each is present, precisely one each of polyols A1d, A1e and A1f. It is furthermore preferable for no further polyols to be present in addition to A1a, A1b and A1c and, if each is present, A1d, A1e and A1f, in other words in preferred embodiments the polyol mixture A1 consists of a maximum of six polyols.
It is generally advantageous for the isocyanate-reactive composition A also to contain further components in addition to the polyol mixture comprising A1. Such components are known in principle to the person skilled in the art and encompass for example water, foam stabilisers, catalysts, flame retardants and optionally further auxiliary substances and additives. In particularly preferred embodiments the isocyanate-reactive composition A additionally comprises
The water fulfils the function of a chemical co-blowing agent, i.e. the reaction with the isocyanate groups releases carbon dioxide, which acts as a blowing agent in addition to T.
In order to establish a stable emulsion it is furthermore advantageous to adhere to certain proportions of blowing agent T to the polyol mixtures A1. In preferred embodiments the invention thus relates to an emulsion in which the mass ratio of A1:T is preferably ≧5:1 to ≦12:1, more preferably ≧10:1 to ≦5:1, most preferably ≧9:1 to ≦6:1.
In preferred embodiments of the emulsion according to the invention the components of the isocyanate-reactive composition A are present in the following percentages by mass, relative in each case to the total mass of the isocyanate-reactive composition A:
Polyol A1a from 5 mass % to 60 mass %, preferably from 15 mass % to 50 mass %,
Polyol A1b from 5 mass % to 60 mass %, preferably from 10 mass % to 50 mass %,
Polyol A1c from 5 mass % to 60 mass %, preferably from 15 mass % to 50 mass %,
Polyol A1d from 0 mass % to 20 mass %, preferably from 0 mass % to 15 mass %,
Polyol A1e from 0 mass % to 20 mass %, preferably from 0 mass % to 15 mass %,
Polyol A1f from 0 mass % to 20 mass %, preferably from 0 mass % to 15 mass %,
Water A2 from 0 mass % to 5 mass %, preferably from 0.5 mass % to 3 mass %,
Foam stabiliser A3 from 1 mass % to 10 mass %, preferably from 1.5 mass % to 8 mass %,
Catalyst A4 from 0.5 mass % to 5 mass %, preferably from 1 mass % to 4 mass %.
The emulsion according to the invention preferably contains the polyol mixture A1 in a percentage by mass of 80 mass % to 90 mass % and the physical blowing agent T in a percentage by mass of 10 mass % to 20 mass %, relative in each case to the total mass of the emulsion.
If several representatives of a component are present (e.g. a mixture of two physical blowing agents T, T1 and T2), the aforementioned percentages by mass apply to the sum of the representatives of a component (i.e. in the above example of two physical blowing agents T, the sum of the percentages by mass of T1 and T2 in the emulsion is 10 mass % to 20 mass %).
In particularly preferred embodiments no further components are present, in other words the emulsion particularly preferably consists at most of A1a, A1b, A1c, A1d, A1e, A1f, A2, A3, A4 and T. The emulsion exceptionally particularly preferably consists of A1a, A1b, A1c, A2, A3, A4 and T.
The production of the emulsions according to the invention preferably takes place in a manner such that the individual components of the polyol mixture A1 (i.e. at least polyols A1a, A1b and A1c, optionally further polyols and optionally auxiliary substances and additives as defined above) are mixed together in any order, generally at atmospheric pressure and temperature, and then the blowing agent T is added to the polyol mixture A1 thus obtained.
The emulsions may be prepared by mixing the components for A in arbitrary order, in general at room temperature and ambient pressure and then adding the blowing agent T. The emulsifying may take place using a high shear mixer such as a jet dispergator or a rotor dispergator. Representative examples include those published in Schubert, H. (editor); Emulgiertechnik; R. Behr's Verlag, Hamburg, 2005.
The emulsions according to the invention are characterised by high stability, without this having to be bought at the price of an excessively increased viscosity. “Stable” is understood to mean here that the emulsion can be stored for at least 2 hours, preferably for at least 1 day, particularly preferably for at least 3 days, most particularly preferably for at least 5 days, at room temperature and under normal pressure, without a phase separation of the polyol mixture A1 and blowing agent T occurring. The viscosity of the polyol mixture A1 according to the invention at 25° C. of ≧1000 mPas to ≦18000 mPas, particularly preferably ≧1500 mPas to ≦12000 mPas and most particularly preferably ≧2000 mPas to ≦12000 mPas. The viscosity is determined in accordance with EN ISO 3219 in the October 1994 version.
The invention also provides a method for producing a polyurethane-containing polymer C, in which an isocyanate component B is reacted with an emulsion according to the invention comprising the polyol mixture A1 and a physical blowing agent T. The production of polyurethane-containing polymers from isocyanate components and isocyanate-reactive components in the presence of blowing agents and optionally further auxiliary substances and additives is known in principle to the person skilled in the art and has already been described many times. The polyurethane-containing polymers C are preferably produced by methods known to the person skilled in the art. Examples are described in U.S. Pat. No. 2,764,565, in G. Oertel (Ed.) “Kunststoff-Handbuch”, Volume VII, Carl Hanser Verlag, 3rd edition, Munich 1993, p. 267 to 354, and in K. Uhlig (Ed.) “Polyurethan Taschenbuch”, Carl Hanser Verlag, 2nd edition, Vienna 2001, p. 83 to 102. Foaming of the components to form the polyurethane-containing polymer C can take place in principle in the manner known from the prior art cited by way of example.
In preferred embodiments of the method according to the invention the isocyanate component B is
The reaction of the isocyanate component B with the emulsion A is preferably performed at isocyanate indexes from 95 to 180, preferably from 95 to 150, particularly preferably from 100 to 130. The “isocyanate index” is understood to be the quotient of the amount of isocyanate groups actually used [mol] and the amount of isocyanate groups stoichiometrically required for the complete reaction of all isocyanate-reactive groups [mol], multiplied by 100. Since one mol of an isocyanate group is required for the reaction of one mol of an isocyanate-reactive group,
Isocyanate index=(mols of isocyanate groups/mols of isocyanate-reactive groups)·100
The present invention also provides the polyurethane-containing polymers C obtainable by the method according to the invention described above. Such polyurethane-containing polymers C can be produced by continuous and discontinuous processing methods and are particularly suitable for use as insulating materials.
Discontinuously produced polyurethane-containing polymers C are moulded foams, which are delimited on both the top and bottom by decor layers. Metals, plastics, wood and paper inter alia are suitable as decor layers. Areas of application for such discontinuously produced PUR composite elements that can be cited in particular are the industrial insulation of appliances such as refrigerators, freezers, combined refrigerator-freezers and water heaters, chill containers and cool boxes and also pipes.
Continuously produced polyurethane-containing polymers C are continuously produced PUR foam blocks of defined width and variable thickness, which are preferably delimited on both the top and bottom by décor layers. In certain areas of application (in construction for example), it is however also possible to dispense completely with décor layers. Metals, metal foils, plastics, wood and paper are primarily suitable as décor layers. Areas of application for such continuously produced polyurethane-containing polymers C that can be cited in particular are the industrial insulation of cold stores and thermal insulation in the building sector.
The use of polyurethane-containing polymers in these areas is known in principle to the person skilled in the art and has already been described many times. The polyurethane-containing polymers C according to the invention are exceptionally suitable for these purposes, as they are characterised by low thermal conductivity values, without there being any risk of processing problems in the production of the foams or in their application on suitable substrates (such as refrigerator housings or pipes) due to excessively high viscosities.
The invention is intended to be illustrated in more detail by the examples below.
The polyols were placed in a reaction vessel in accordance with the corresponding formulation (cf. Table 1). The required amounts of additives such as water, catalysts and stabilisers were weighed in individually. Finally cyclopentane as the blowing agent was weighed in, and all components were homogenised for 60 s at 4200 rpm using a standard laboratory stirrer.
The quality of the emulsion was assessed immediately after production by a specialist operator. To this end a drop of the emulsion was applied to a slide and covered with a cover glass. The transmission of the emulsion was estimated by the operator against a backlight. The finer the droplet size and the more homogeneous and narrower their size distribution, the more transparent the examined samples were against a backlight. All samples according to the invention could be clearly recognised as emulsions; complete transparency as in a true solution or a microemulsion was not observed.
Only freshly prepared emulsions (examples 2 to 13) and solutions (example 1, comparison) were processed to make PUR-containing polymers (rigid PUR foams). There was a difference in time of less than one hour between production of the emulsion and its processing. The emulsions and solutions obtained as described above were mixed together using a standard laboratory stirrer at 4200 rpm, reacted and introduced into a mould. The raw material temperature of the isocyanate-reactive composition A including the blowing agent T and of the isocyanate component B was 20° C.; the mould temperature was 40° C. The moulded foams produced in this way were analysed with regard to their core density and thermal conductivity.
The freshly prepared emulsions were stored at 20° C. in order to assess their stability and checked visually every day for phase separation. The quality of an emulsion was evaluated directly after preparation by measuring the droplet size. To this effect, the emulsion was inspected via an optical microscope using bright field transmission microscopy in a layer thickness of the specimen of 20 μm to 40 μm. The microscope used was an Axioplan 2 microscope from Zeiss. Average droplet sizes of a non-aged emulsion thus determined were below 10 μm.
Hydroxyl values (OH values) were determined in accordance with DIN 53240 (December 1971).
Viscosities were determined in accordance with EN ISO 3219 in the October 1994 version.
Thermal conductivity values were determined in accordance with DIN EN 12664 in the May 2001 version and unless otherwise specified were measured at a core temperature of 10° C.
The specified core densities were measured on the cut specimens in order to calculate the thermal conductivity in accordance with DIN EN 12664 in the May 2001 version by determining the corresponding mass.
The formulations are listed in Table 1.
The analyses of the emulsions and of the resulting rigid PUR foams are summarised in Table 2.
Comparative example 1 illustrates a latest-generation formulation that meets the current requirements for insulating materials in the area of application of refrigerators for example. This has already explicitly been optimised to obtain low thermal conductivity values. It is a soluble formulation in which the amount of physical blowing agent used is completely dissolved in the polyol mixture. Positive influences of an emulsion on the nucleating effect of the droplets can thus be excluded completely in this comparison. The comparison is admissible, however, as the reaction profiles of example 1 match those of the subsequent emulsion foamings. Furthermore, comparable density levels were used in the production of the rigid PUR foams.
In all further examples 2 to 13 according to the invention, homogeneous and stable emulsions were foamed with a diisocyanate based on MDI. In comparison to example 1, all PUR foams produced in this way have much lower thermal conductivity values. The thermal conductivity was lowered by between 1 and 1.8 mW m−1K−1. Surprisingly, this clear improvement in thermal conductivity was achieved despite the simultaneous rise in core density of up to 4 kg/m3.
Examples 3, 5, 7, 9 and 13 confirm that the foaming of the emulsions according to the invention with the prepolymer isocyanate 2 likewise leads to an improvement in the thermal conductivity that is comparable to that achieved with isocyanate 1. In the case of example 3, the thermal conductivity was able to be improved by a further 0.6 mW m−1K−1 by replacing isocyanate 1 with isocyanate 2.
Tables 1 and 2 confirm that with the aid of emulsions the thermal conductivity of PUR foams can clearly be improved in comparison to a common soluble polyol formulation. Factors influencing the degree of this improvement are the water content, the viscosity and the content of oxyethylene groups in the polyol formulation. Thus the emulsions shown in examples 10 to 13 lead to a lowering of the thermal conductivity by only 1.0 to 1.2 mW m−1K−1 (albeit associated with a lowering of the viscosity, which is advantageous), whereas in the case of examples 3 to 9 the thermal conductivity was consistently lowered by 1.6 to 1.8 mW m−1K−1.
While it is true that in examples 2 to 9 an increase in viscosity was observed in comparison with example 1, this is still within acceptable limits. As has already been mentioned, a doubling of the viscosity is not unusual in the prior art, and the systems according to the invention are far removed from that.
All the emulsions listed here exhibited good to very good homogeneity and were stable for several days under normal conditions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 081 621.6 | Aug 2011 | DE | national |
| 12155275.6 | Feb 2012 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/066330 | 8/22/2012 | WO | 00 | 2/24/2014 |
