WO2015165870A1

WO2015165870A1 - Method for improving the dimensional stability of polyurethane rigid foams

Info

Publication number: WO2015165870A1
Application number: PCT/EP2015/059136
Authority: WO
Inventors: Joachim KLESER; Uwe Kuenzel; Stephan Schleiermacher; Lutz Brassat
Original assignee: Covestro Deutschland Ag
Priority date: 2014-04-30
Filing date: 2015-04-28
Publication date: 2015-11-05

Abstract

The invention relates to a method for improving the dimensional stability of shaped bodies made of polyurethane rigid foam comprising the following steps: • a) providing a shaped body made of polyurethane rigid foam, • b) intermediate storage of the shaped body at a water vapour pressure p_z of < 0.12 bar and at a temperature T_z ≤ 70 ºC for at least 5 hours, • c) conditioning the shaped body at a water vapour pressure p_K of ≥ 0.12 bar and at a temperature T_κ ≥ 50 ºC. The invention also relates to a shaped body made of polyurethane rigid foam which is obtained according to this method, and the use thereof as a construction element.

Description

Process for improving the dimensional stability of rigid polyurethane foams

The invention relates to a method for improving the dimensional stability of PUR and PIR rigid foams. The invention also relates to a molded article of PUR and PIR rigid foams, which is obtainable by this method and its use. PUR and PIR rigid foams, collectively referred to as PU hard foam, are used in construction as thermal insulation materials according to the standard DIN EN 13 165. This standard specifies the requirements for factory made rigid polyurethane foam products with and without lamination or coating used for the thermal insulation of buildings. The products are produced in the form of plates and are used primarily to reduce heat and cold losses from the building. Since they reduce the energy expenditure of the heating or cooling system in this respect, such insulation contributes to the protection of the environment. However, it has been shown that climatic fluctuations and the effect of temperature and humidity can lead to changes in the size of the elements. This can lead, inter alia, to unwanted stresses in the functional layers of buildings created with the elements and to offsets between individual elements and associated optical defects. This is disadvantageous in particular if the elements are used as insulation panels, since potential cold bridges can thus be formed between the gaps. Heat-insulating composite systems generally have a firmly bonded plaster layer, so that dimensional changes of the boards can lead to cracks in the plaster layer. The permissible maximum values for the dimensional change of rigid polyurethane foams are specified in the standard DIN EN 13 165.

To achieve a continuous thermal or cold insulation, it is desirable to improve the dimensional stability of the aforementioned rigid foams even under changing climatic conditions, that is, in particular when exposed to changing temperatures and / or changing air humidity.

US Pat. No. 3,243,492 describes a process for the production of rigid PU foams, in which the produced plates pass through a stabilization zone immediately after manufacture, in which a treatment at elevated temperature and a relative humidity of 30-95% at a vapor pressure of 145 to 760 mm Hg he follows. Due to the continuous process control, however, a preferred extended storage of the plates is not possible because the residence time in the stabilization zone is limited in time.

A disadvantage of the known methods is further that the dimensional stability of the foam panels is not satisfactory in every respect. The object of the present invention was to provide a method which allows over the prior art, an improvement in the dimensional stability of moldings made of PU rigid foams under temperature and humidity.

This object is achieved by a method for improving the dimensional stability of moldings of rigid polyurethane foam comprising the following steps:

Step a) providing a shaped body of rigid polyurethane foam, followed by the steps b) and c), and optionally step d), wherein

Step b) the treatment of the shaped article by storage at a water vapor pressure pz of <0.12 bar and a temperature Tz <70 ° C for a period of time tz ("intermediate storage") and step e) the subsequent treatment of the shaped article by storage at a water vapor pressure ρκ> 0.12 bar and a temperature Τκ> 50 ° C ("conditioning"), as well as

Step d) optionally a subsequent storage of the molding at the respective ambient temperature and humidity ("reconditioning") comprise, characterized in that in step b) a time tz of at least 5 hours is maintained.

The invention will be explained in detail below. Various embodiments can be combined with one another as desired, as long as the opposite does not clearly result for the person skilled in the art from the context.

The shaped body used in the process according to the invention is typically produced in a manner known per se by chemical reaction of at least one polyol compound with at least one polyisocyanate compound. In a preferred embodiment, the process according to the invention is carried out directly after the production of the shaped body.

The present invention is based on the finding that in freshly produced moldings of rigid polyurethane foam by intermediate storage for at least 5 hours at a water vapor pressure of less than 0.12 bar and a temperature of at most 70 ° C, in particular room temperature, and subsequent conditioning at increased temperature and increased humidity, increased dimensional stability of the molding can be achieved. In particular, for long periods of interim storage of the moldings, it is surprisingly found that the dimensional stability of the treated moldings is markedly improved at elevated air humidity and elevated temperature compared to not Conditioned moldings or conditioned moldings, which experienced only a short intermediate storage.

The improvement in dimensional stability achieved by the process according to the invention can advantageously be verified by subjecting the conditioned shaped body to a temperature of 70 ° C. and a relative humidity of 95% relative humidity for a period of 24 to 48 hours following the process (" Weathering ") This measure simulates the behavior of an insulation board when installed under extreme climatic conditions.

In an advantageous embodiment, the process according to the invention gives a conditioned molded body of rigid polyurethane foam which under climatic variations / weathering has a dimensional change of less than 2.5%, preferably less than 1.5% and particularly preferably less than 1%, based on at least one component dimension has.

In one embodiment of the invention, the treatment of the molding in step b) of the process according to the invention at a water vapor pressure p _z <0.12 bar, preferably <0.08 bar, more preferably <0.06 bar and a temperature T _z <70 ° C, preferably <55 ° C, more preferably <35 ° C. In an advantageous embodiment, the treatment of the shaped body in step b) takes place at room temperature.

For the treatment of the shaped body in step b) in the form of an intermediate storage, a time tz of at least 5 hours is maintained according to the invention. According to the invention, the time duration tz denotes the period beginning with the foaming time until the subsequent conditioning of the shaped body in step c). Preferably, the time tz is more than 12 hours, more preferably more than 24 hours and most preferably more than 48 hours. The conditioning of the shaped body in step c) takes place according to the invention at a water vapor pressure ρκ of> 0.12 bar, preferably of> 0.2 bar, more preferably of> 0.3 bar at a temperature Τκ of at least 50 ° C, in particular at least 60 ° C, preferably at least 65 ° C and more preferably at least 70 ° C. In general, it is preferred that the temperature Τκ during conditioning does not exceed 100 ° C. In an advantageous embodiment, T _{K is} therefore <100 ° C, in particular <90 ° C.

The abovementioned preferred value ranges for the water vapor pressures and temperatures during the conditioning in step c) are advantageously distinguished by the fact that the dimensional stability of the correspondingly treated molding is markedly improved. This applies in particular to the combination of a temperature Τκ of at least 70 ° C at a water vapor pressure ρκ of> 0.24 bar (corresponding to a relative humidity of at least 80% RH), and in particular at a water vapor pressure ρκ of> 0.27 bar (corresponding a relative humidity of at least 90% RH). The duration for efficient conditioning of the shaped body in step c) (duration ίκ) depends on the chosen conditioning conditions, ie the prevailing water vapor pressure ρκ and the temperature Τκ during the conditioning. In general, the value pair of pi and Τκ is adjusted so that the desired conditioning effect is achieved after a period of time ίκ, which can be, for example, between about 5 h to 24 h. In the method according to the invention, the intermediate storage and the conditioning of the shaped body in steps b) and c) of the process according to the invention at fixed water vapor pressures and temperatures in principle be carried out in any manner known to the skilled person, wherein the use of a climate chamber is most convenient because in a such that the control of the vapor pressure can be made precisely. The climatic chamber to be used for this purpose is equipped with a thermostatic control unit and a humidity control unit. In an advantageous embodiment of the invention, the conditioning of the shaped body in step c) is therefore carried out in a climatic chamber.

The relative humidity (r.F.) indicates for the current temperature and the current pressure the ratio of the instantaneous water vapor content to the maximum possible water vapor content and is defined as the percentage ratio between the absolute humidity and the maximum humidity, or analogously between vapor pressure / saturation vapor pressure.

Usually, the intermediate storage and the conditioning are carried out under atmospheric pressure. However, it is also conceivable according to the invention that these steps are carried out under a slight overpressure or underpressure. The molded articles treated by the process according to the invention can be used directly after completion of the treatment or can also be cut to the desired level after the treatment.

In the method according to the invention, moreover, after step c), the molding can be "reconditioned" at ambient temperature and ambient humidity, in particular at 23 ° C. +/- 5 ° C. and 50% +/- 10% relative atmospheric humidity (step d)). In particular, if the preceding conditioning is carried out at relatively high humidities / temperatures, this can lead to water condensing in a subsequent rapid cooling of the molded body, in particular in the region of the foam cells (micro), so that a subsequent Reconditioning is beneficial here. If appropriate, steps b) and / or c) can subsequently be repeated. This procedure can also be carried out several times in succession, for example once, twice or even three times.

PU rigid foams are understood to mean those rigid polyurethane foams which contain urethane structures and optionally isocyanurate structures. Reaction systems for PU rigid foams are particularly suitable for the production of rigid polyurethane foam products, such as polyurethane insulation boards, metal composite elements and polyurethane block foam.

The aforementioned rigid foams are known to be composed of at least one polyisocyanate component and at least one component with isocyanate-reactive groups.

The organic polyisocyanate component contains aromatic polyisocyanates.

Preference is normally given to those polyisocyanates which are technically readily available. These include, in particular, isomeric methyldiphenyl diisocyanates and their higher homologs, the polyphenyl polymethylene polyisocyanates. Both are obtained by aniline-formaldehyde condensation and subsequent treatment with phosgene (crude MDI). Also preferred are polyisocyanates derived from 4,4'- and / or 2,4'-diphenylmethane diisocyanate and / or 2,2'-diphenylmethane diisocyanate and their homologs, the carbodiimide, urethane, allophanate, isocyanurate, urea or biuret groups contained (modified polyisocyanates). For the production of PU rigid foams, the organic polyisocyanate component used is preferably mixtures of isomers of diphenylmethane diisocyanate (MDI) and its oligomers. Such blends are generally referred to as "polymeric MDI" (pMDI) Moreover, it is possible to use suitable NCO prepolymers formed via reaction of polymeric MDI with aliphatic and / or aromatic polyether polyols, polyester polyols, polyether polyester polyols, and / or polyether carbonate polyols can.

As the isocyanate-reactive component, there may be included, among others, polyols, polyether polyols, polyester polyols, polyetherester polyols, polyethercarbonate polyols, and combinations thereof. Preferred polyether polyols are addition products of ethylene oxide and / or propylene oxide, and / or epichlorohydrin to di- or polyfunctional starter molecules. Suitable starter molecules are, for example, water, ethylene glycol, diethylene glycol, butyl diglycol, glycerol, diethylene glycol, trimethylolpropane, propylene glycol, dipropylene glycol, pentaerythritol, sorbitol, sucrose, ethylenediamine, toluenediamine, triethanolamine, 1,4-butanediol, 1,6-hexanediol and low molecular weight, hydroxyl groups having esters of such polyols with dicarboxylic acids. Suitable polyester polyols include polycondensates of di- as well as tri- and tetraols and di- and furthermore tri- and tetracarboxylic acids or hydroxycarboxylic acids or lactones. Instead of the free polycarboxylic acids, it is also possible to use the corresponding polycarboxylic acid anhydrides or corresponding polycarboxylic acid esters of lower alcohols for the preparation of the polyesters. Examples of suitable diols are ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycols such as polyethylene glycol, furthermore 1, 2-propanediol, 1,3-propanediol, butanediol (1,3), butanediol (1,4), hexanediol (1,6) and isomers, neopentyl glycol or hydroxypivalic acid neopentyl glycol esters. In addition, it is also possible to use polyols, such as trimethylolpropane, glycerol, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurate. Examples of suitable polycarboxylic acids are phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, tetrachlorophthalic acid, maleic acid, fumaric acid, itaconic acid, malonic acid, suberic acid, 2-methylsuccinic acid, 3,3-diethylglutaric acid, 2 2-dimethyl succinic acid, dodecanedioic acid, endomethylenetetrahydrophthalic acid, dimer fatty acid, trimer fatty acid, citric acid, or trimellitic acid. The acid source used can also be the corresponding anhydrides, for example phthalic anhydride.

Useful polyetherester polyols are those compounds containing ether groups, ester groups and OH groups.

Polyether carbonate polyols are obtainable by addition of carbon dioxide and alkylene oxides to suitable H-functional starter substances.

Flame retardants may be added to the polyol component, preferably in an amount of from 5 to 50% by weight, based on the total amount of compounds having isocyanate-reactive hydrogen atoms in the polyol component, in particular from 7 to 40% by weight, particularly preferably from 12 to 30% by weight. -%. Such flame retardants are known to those skilled in principle and described for example in "Plastics Handbook", Volume 7 "Polyurethane", Chapter 6.1. These may be, for example, bromine- and chlorine-containing polyols or phosphorus compounds such as the esters of orthophosphoric acid and metaphosphoric acid, which may also contain halogen. Preferably, liquid flame retardants are selected at room temperature. Is used as much blowing agent and co-blowing agent, as is necessary to achieve a dimensionally stable foam matrix and desired density. The proportion may be, for example, from 0 to 6.0% by weight of co-propellant and from 1.0 to 30.0% by weight of propellant, in each case based on 100% by weight of polyol component. The proportion of co-propellant to propellant may be from 20: 1 to 0: 100 as needed.

As propellants, hydrocarbons, e.g. the isomers of pentane, or fluorohydrocarbons, e.g. HFC 245fa (1,1,1,3,3-pentafluoropropane), HFC 365mfc (1,1,1,3,3-pentafluorobutane) or mixtures thereof with HFC 227ea (heptafluoropropane), or fluorinated olefins, e.g. Trans-chloro-3,3,3-trifluoropropene and cis-l, l, l, 4,4,4-hexafluoro-2-butene used. It is also possible to combine different propellant classes.

The co-blowing agent used is preferably water, preferably in an amount of up to 6% by weight, particularly preferably 0.5 to 4% by weight, based on the total amount of compounds having isocyanate-reactive hydrogen atoms in the polyol component.

The polyol component is conveniently added in polyurethane chemistry conventional catalysts. The amine catalysts necessary for producing a PU rigid foam and the salts used as trimerization catalysts are used in amounts such that e.g. On continuous production lines elements with flexible cover layers can be produced with speeds of up to 60 m / min depending on the element thickness as well as for insulation on pipes, walls, roofs and tanks and in refrigerators in the spray foam process with sufficient curing time can be produced. A discontinuous production is possible.

Examples of such catalysts are: triethylenediamine, Ν, Ν-dimethylcyclohexylamine, tetramethylenediamine, 1-methyl-4-dimethylaminoethylpiperazine, triethylamine, tributylamine, dimethylbenzylamine, Ν, Ν ', Ν "-tris (dimethylaminopropyl) hexahydrotriazine, Dimethylaminopropylformamide, Ν, Ν, Ν ', Ν'-tetramethylethylenediamine, Ν, Ν, Ν', Ν'-tetramethylbutanediamine, tetramethylhexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, dimethylpiperazine, 1, 2-dimethylimidazole, 1-azabicyclo [3.3. 0] octane, bis (dimethylaminopropyl) urea, N-methylmorpholine, N-ethylmorpholine, N-cyclohexylmorpholine, 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, triethanolamine, diethanolamine, triisopropanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, dimethylethanolamine, stannous acetate, stannous octoate, stannous ethylhexoate, stannous laurate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dioctyltin diacetate, Tris- (N, N-dimethylaminopropyl) -s-hexahydrotriazine, Tet ramethyl ammonium hydroxide, sodium acetate, sodium octoate, potassium formate, potassium acetate, potassium octoate, sodium hydroxide or mixtures of these catalysts. Furthermore, foam stabilizers may be added to the polyol component, for which purpose polyethersiloxanes are particularly suitable. These compounds are generally designed so that a copolymer of ethylene oxide and propylene oxide is connected to a Polydimethylsiloxanrest. Such substances are available on the market for example under the name Struksilon 8031 from the company Schill and Seilacher. Even silicone-free stabilizers, such as the product LK 443 from Air Products, can be used.

Furthermore, in the reaction system according to the invention, the organic polyisocyanate cyanate component and the polyol component in such a ratio to each other that results in a ratio of 100 to 600, in particular from 200 to 600. Under code is multiplied by 100 ratio of the mass actually used Isocyanate understood to stoichiometrically required mass of isocyanate. The stoichiometrically required mass of isocyanate corresponds to that mass of isocyanate in which exactly one NCO-reactive group exists in the reaction system for each NCO group.

The preparation of the rigid PU foams according to the invention is typically carried out by the one-step process known to those skilled in the reaction in which the reaction components are reacted continuously or discontinuously with each other and then subsequently either manually or by means of mechanical equipment in high-pressure or low-pressure process after discharge to a conveyor belt or be made into suitable forms for curing. Examples are described in US-A 2,764,565, in G. Oertel (ed.) "Plastics Handbook", Volume VII, Carl Hanser Verlag, 3rd edition, Munich 1993, p 267 ff, and in K. Uhlig (ed .) "Polyurethane paperback", Carl Hanser Verlag, 2nd edition, Vienna 2001, pp. 83-102 described. In a preferred embodiment, the rigid polyurethane foam is produced in a continuous process.

The molded body of rigid polyurethane foam may have flexible and / or rigid cover layers. As flexible cover layers can be used for example: mineral nonwovens (eg glass fiber fabric), paper topcoats, flexible metal foils (eg 50 μιη AI film) or multilayer films (eg one or more thin AI films paper and PE film). The moldings according to the invention may also be in the form of a sandwich composite element consisting of a rigid and a flexible or two rigid cover layers and a core layer lying therebetween. In particular, metal (foam) composite elements consist of at least two metal cover layers and a foam core layer. Further layers may be provided between the core layer and the cover layers. For example, the outer layers, for example, with a paint, coated. In the context of the method according to the invention, it is particularly preferred that the molded body of rigid PU foam is closed-cell, wherein the proportion of open cells is at most 10% of the total cell volume, in particular at most 7%. The measurement is carried out according to DIN ISO 4590 "Determination of the volume fraction of open and closed cells in hard foams".

The rigid PU foam preferably has a core density of> 26 kg / m ³ to <50 kg / m ³ . The core density is determined according to DIN EN 1602: 1996. Preferably, the core density is in a range of> 27 kg / m ³ to <45 kg / m ³ and particularly preferably from> 29 kg / m ³ to <42 kg / m ³ . Another object of the present invention relates to a molded body of rigid polyurethane foam, which is obtainable by a process according to the invention.

The conditioned moldings can be used in applications in which the dimensional stability of the components used is of great importance. This is an example of thermal insulation elements of walls, floors and roofs, especially flat roofs or when used in thermal insulation systems of the case.

Another object of the present invention is the use of the inventive shaped molded body made of rigid polyurethane foam as a construction element, in particular for the thermal insulation of the building envelope.

The present invention will be further discussed below by way of examples.

Examples:

Examples 1 to 5:

Formulation PU rigid foam / in parts by weight: Polyol formulation A:

- 63.8 parts by weight of polyester polyol of phthalic anhydride, diethylene glycol and

Ethylene glycol, functionality 2, OH number 240 mg KOH / g

5 parts by weight of polyether polyol of trimethylolpropane, ethylene oxide and propylene oxide, functionality 3, OH number 255 mg KOH / g

2.2 parts by weight of polyesterpolyol from phthalic anhydride and diethylene glycol, functionality 2, OH number 705 mg KOH / g:

20 parts by weight of trischloroisopropyl phosphate (flame retardant)

5 parts by weight of triethyl phosphate (flame retardant)

4 parts by weight of silicone stabilizer

5 parts by weight of catalyst (25% by weight of potassium acetate in 75% by weight of diethylene glycol)

Recipe 1:

105 parts by weight of polyol formulation A,

15.9 parts by weight of blowing agent: n-pentane,

194 parts by weight of polyisocyanate polymer MDI with 31 wt.% NCO, covering layer:

"Aluminum strip 99/52, hard, glossy / matt, both sides painted with 310g 743, coined with coarse coarse grain" (manufacturer: Hydro Aluminum Rolled Products GmbH) .The B side of the rolled-up aluminum strip pointed to the steel cylinder the B-side applied

Two-sided aluminum-laminated rigid polyurethane foam panels were produced continuously on a double belt according to recipe 1 and immediately cut to length and trimmed to 600 mm × 600 mm × 100 mm.

The edged moldings were stored for a period of time tz (see Table 1) measured from the foaming time at a water vapor pressure pz of 0.01 bar and a temperature of 23 ° C (corresponding to a relative humidity of 50% RH). Subsequently, the moldings were trimmed to 90 mm x 90 mm x 100 mm and at a water vapor pressure p _K of 0.3 bar and a temperature T _K of 70 ° C (corresponding to a relative humidity of 95% RH) for a period of 20 hours conditioned in a climatic chamber made by Espec, model PL-4KPH. Finally, the moldings were reconditioned for a period of 7 days at a temperature of 23 ° C and a relative humidity of 50% RH.

Dimensional stability measurements:

Subsequently, the conditioned moldings were stored for 24 h at a temperature of 70 ° C and a relative humidity of 95% RH. The effect of the above-described steps was checked by measuring the dimensional changes of length LI, width L2 and thickness D of the moldings with a caliper each before and after this storage. The relative change of the dimension compared to the zero value has been documented.

* Specification for experiment 5 in days. ** RH: relative humidity. Table 1: Dimensional stability of the conditioned moldings.

The series in Table 1 shows the advantageous effect of a prolonged intermediate storage time, in particular on the component thickness change D. A molded body, which was subjected to the subsequent conditioning after a longer intermediate storage time, shows a significantly smaller dimensional change in the subsequent measurements (experiment 5).

Examples 6 to 10:

Formulation PU rigid foam:

Polyol formulation B:

- 72.8 parts by weight of polyester polyol from phthalic anhydride and diethylene glycol functionality 2, OH number 240 mg KOH / g

20.4 parts by weight of trischloroisopropyl phosphate (flame retardant)

2.1 parts by weight of silicone stabilizer

2.8 parts by weight of catalyst from 25% by weight of potassium acetate in 75% by weight of diethylene glycol - 0.7 parts by weight of catalyst dimethylcyclohexylamine

Recipe 2:

100 parts by weight of polyol formulation B,

16.7 parts by weight of blowing agent: n-pentane,

218.3 parts by weight of polyisocyanate polymer MDI with 31 wt .-% NCO,

Top layer:

"Aluminum strip 99/52, hard, gloss / matt, both sides painted with 310g 743, coined with coarse coarse grain" (manufacturer: Hydro Aluminum Roiled Products GmbH) .The B side of the rolled up aluminum strip pointed to the steel cylinder applied the B-side.

Production of the moldings

Analogously to Examples 1 to 5 aluminum-laminated PU foam boards were prepared on both sides according to the recipe 2. They were then immediately cut to length and trimmed to 600 mm x 600 mm x 100 mm and left at this size for the following tests.

The edged moldings were stored for a period of time tz (see Table 2) measured from the foaming time at a water vapor pressure pz of 0.01 bar and a temperature of 23 ° C (corresponding to a relative humidity of 50% RH). Subsequently, the moldings were conditioned at a water vapor pressure p _K of 0.28 bar and a temperature Τκ of 70 ° C (corresponding to a relative humidity of 90% RH) for a period of 24 hours in a climate chamber Espec, model PL-4KPH ,

Finally, the moldings were reconditioned for a period of 7 days at a temperature of 23 ° C and a relative humidity of 50% RH.

Dimensional stability measurements:

Subsequently, the conditioned moldings were stored for 48 h at a temperature of 70 ° C and a relative humidity of 95% RH. Analogous to Examples 1 to 5, the dimensional changes of length LI, width L2 and thickness D of the shaped bodies were respectively measured before and after this storage and documented.

Table 2: Dimensional stability of the conditioned shaped bodies.

▲ length [%]

• width [%]

♦ Thickness {%}

Length of blank sample [%]

Width blank test [%]

Thickness blank [%]

0 50 100 150 200

Duration of intermediate storage [h]

Figure 1: Graphs to Table 2

The series of Table 2 also shows that moldings which have been stored according to the invention have an improvement in the dimensional stability, in particular with regard to the component thickness change D, this effect increasing with the duration of the intermediate storage.

Claims

claims

Process for improving the dimensional stability of PU rigid foam moldings comprising the following steps:

Step b) the treatment of the shaped body by storage at a water vapor pressure pz of <0.12 bar and a temperature Tz <70 ° C for a period tz and

Step c) the subsequent treatment of the molding by storage at a water vapor pressure ρκ of> 0.12 bar and a temperature T _K > 50 ° C, and

Step d) optionally comprise a subsequent storage of the shaped body at the respective ambient temperature and humidity, characterized in that in step b) a time tz of at least 5 hours is maintained.

2. The method according to claim 1, characterized in that step c) takes place at a temperature TK of at least 60 ° C, in particular at least 65 ° C, preferably at least 70 ° C.

3. The method according to claim 1 or 2, characterized in that step c) takes place at a water vapor pressure ρκ of> 0.12 bar, preferably of> 0.2 bar, more preferably of> 0.3 bar.

4. The method according to any one of the preceding claims, characterized in that the conditioning of the shaped body in step c) takes place in a climatic chamber.

5. The method according to any one of the preceding claims, characterized in that the shaped body is provided in step a) by chemical reaction of at least one polyol compound with at least one polyisocyanate compound.

6. The method according to any one of the preceding claims, characterized in that the shaped body is a closed-cell shaped body, wherein the proportion of open cells is at most 10% of the total cell volume, in particular at most 7%.

7. The method according to any one of the preceding claims, characterized in that the shaped body has a core density of> 26 kg / m ³ to <50 kg / m ³ .

8. The method according to any one of the preceding claims, characterized in that the shaped body has at least one flexible and / or rigid cover layer.

9. molded body of rigid polyurethane foam, obtainable by a process according to one of claims 1 to 8.

10. Use of moldings of rigid polyurethane foam according to claim 9 as a construction element, in particular for the thermal insulation of the building envelope.