CA2155877A1

CA2155877A1 - Prepolymer composition for insulating foams

Info

Publication number: CA2155877A1
Application number: CA002155877A
Authority: CA
Inventors: Mathias Pauls; Rene Schumacher
Original assignee: Individual
Current assignee: Rathor AG
Priority date: 1993-02-10
Filing date: 1994-02-10
Publication date: 1994-08-18

Abstract

Prepolymer composition for preparing polyurethane insulating foams from pressurized containers consists of a prepolymer component with at least one polyurethane prepolymer containing 4 to 20% by weight NCO groups, and usual additives, as well as a propellant gas. A
polyisocyanate is used containing less than 2% by weight of a monomer isocyanate, with respect to the prepolymer component.

Description

21~5877 -Description This invention relates to a prepolymer composition for producing polyurethane insulating foams from ~/ pressure tanks which consists of a prepolymer component with at least one PU prepolymer with a content of NCO groups of 4 to 20 wt%
and usual additives as well as a propellant component. The invention furthermore relates to the use of polyisocyanate prepolymers based on hexamethylene-1,6-diisocyanates for pro-ducing prepolymer components for pressure-can polyurethane insulating foams, as well as to pressure cans with such a prepolymer composition and optionally a separate polyol com-ponent for producing polyurethane insulating foams.
The inventive prepolymer composition is used for produc-ing polyurethane insulating foams which are used particularly for foaming in cavities. The main areas of application are the construction industry, but also technical products in which cavities must be filled to avoid condensation nests.
When one-component polyurethane foams are spoken of, these are applied by discharging the prepolymer composition from pressure tanks, for example aerosol cans, on the spot with the help of propellants with a bulk density of 10 to 50 g/l, and processed. lC foams are moisture-hardening, i.e. they can be cured solely with the help of the moisture contained in the air.
Two-component polyurethane foams require a second hy-droxy component for curing the prepolymer composition, gener-ally a polyol which must be added directly before foam forma-tion. Curing can be accelerated by catalysts. Bulk densities in 2C foams are characteristically 10 to 100 g/l.
Transitional forms between lC and 2C foams are possible.
In this case a quantity of a hydroxyl component insufficient for reacting the isocyanate groups is added to the prepolymer before discharge. These transitional forms have come to be known as "1.5C foams". The invention also covers foaming agents with more than one separate reactive component.

AMENDED SHEET

- 213~877 Conventional prepolymer compositions for polyurethane insulating foams contain a prepolymer component having a minimum content of reactive NCO groups. The prepolymer itself is a polymer of suitable viscosity with terminal NCO groups.
The composition contains a certain quantity of monomeric iso-cyanate. Suitable isocyanates are for example isophorone di-isocyanate, referred to as IPDI, tolylene diisocyanate, also referred to as TDI, diisocyanatotoluene, 1,5-diisocyanato-naphthalene, referred to as NDI, triisocyanatotrimethyl-methane, 1,6-diisocyanatohexane, referred to as HDI, or 4,4-diisocyanatodiphenylmethane in a raw and pure form or as a mixture. An especially common one is 4,4-diisocyanatodi-phenylmethane, also referred to as MDI, which is used both in a raw form (raw MDI) and in the form of pure 2,4- and 4,4-isomers or mixtures thereof. One can likewise use the two common TDI isomers alone or in a mixture. For producing the prepolymer component one reacts such isocyanates with hydroxy polyethers, polyesters or polyvalent alcohols, making sure the prepolymer acquires a viscosity suitable for the composi-tion.
As mentioned above, PU prepolymers suitable for produc-ing polyurethane insulating foams from pressure tanks contain a residual content of unreacted monomeric isocyanate which can be up to 40%. This residual content is usually due to manufacturing, but is also desirable since it has turned out that this residual content has a positive effect on the serv-iceability, in particular the inherent and dimensional sta-bility, of the produced foams. On the other hand monomeric isocyanates are deemed dangerous substances subject to iden-tification because of their toxicity, despite their generally rather low volatility. MDI, the preferred initial isocyanate for lC foams, is subject to a maximum working place concen-tration of 0.01 ppm, as is HDI. Because of the toxicity of the contained substances packings having residues of these prepolymers are subject to cost-intensive restrictions on disposal.

21~5877 Although it is possible to produce prepolymers with low residual monomer contents, the low serviceability of the pro-duced foams has prevented the use of such prepolymer composi-tions up to now. No applicable polymer compositions for pres-sure cans have become known. It was generally assumed that monomer-free standardizations cannot be used in pressure cans. Monomer-free prepolymers can be produced for example by removal of the monomer through distillation and optionally further reacti`on with a reactive hydroxy polyether and/or ~olve~ter ~n~/or veaetable oil, modified or unmodified. __ EP-A-0 420 026 describes a method for producing low-monomer polyurethane prepolymer based on tolylene diisocya-nate. DE-A-40 25 843 and EP-A-0 480 342 describe prepolymer compositions for producing polyurethane insulating foams from pressure tanks which consist of a prepolymer component with at least one PU prepolymer with free NCO groups and usual ad-ditives as well as a propellant component. Low-monomer pre-polymer components are accordingly not used.

- 3 ~ 21~S877 Although it is possiblc to produce ~lepGl~ el5 wiLl~ low residual monomer contents, the low serviceability of ~ -duced foams has prevented the use of such prep ~ composi-tions up to now. No applicable polyme ~ itions for pres-sure cans have become known. ~ generally assumed that monomer-free standard ~ cannot be used in pressure cans. Monomer- ~ epolymers can be produced for example by remova ~ e monomer through distillation and optionally ~ er reaction with a reactive hydroxy polyether and/or _ ~ polyc~tcr and/or vcgctablc oil, modificd or unmodificd.
In view of the disadvantages of known PU prepolymers containing monomeric isocyanate it is desirable to provide a PU prepolymer containing little or substantially no more monomeric isocyanate while guaranteeing the properties de-manded particularly by the construction industry, e.g. dimen-sional stability of the foam. It is in particular the goal of the invention to provide a prepolymer composition for dimen-sionally stable 1.5C PU foams which contains toxic and/or ir-ritant components in quantities so low that they are no longer subject to identification.
In addition there is a need for additives promoting the dimensional stability of insulating foams to be used for monomer-containing as well as low-monomer and monomer-free prepolymers.
The invention provides a prepolymer composition of the abovementioned type which is based on the use of a polyisocy-anate with a content of less than 2 wt%, based on the pre-polymer component, of monomeric isocyanate. This surprisingly achieves applicable mixtures.
For producing the inventively applied prepolymer compo-sition one uses conventional aliphatic and aromatic polyiso-cyanates. In particular one uses polyfunctional isocyanates with a mean of 2 to 4 isocyanate groups, both in monomeric and in oligomeric form. As stated at the outset, these pre-polymer compositions are themselves reaction products from monomers or oligomers containing isocyanate groups, and com-~ 4 - 21S~87~

ponents reactive therewith, in particular hydroxyfunctional compounds. Suitable initial isocyanates are mentioned for ex-ample in DE-A-42 15 467.
Especially suitable isocyanate prepolymers for these prepolymer compositions are ones based on HDI, dimeric or trimeric TDI, NDI, 4,4'-dicyclohexylmethanediisocyanate and IPDI, which can be converted especially easily to substan-tially monomer-free prepolymers. It is also especially suit-able to use polyisocyanates containing biuret groups (Desmo-dur N with 22% NCO content, optionally after lowering the NCO
content by dilution) and addition polymers of TDI with poly-ols, in particular trimethylolpropane (Desmodur L with 13%
NCO) which are set to be substantially monomer-free. Further suitable types of isocyanate are the commercial products Des-modur Z 4370 and E 3265.
The NCO content in the applied prepolymer is between 4 and 20 wt%, preferably between 6 and 18 wt% and in particular between 7 and 13 wt%.
When producing the isocyanate prepolymers one uses usual hydroxy components, for example polyether, polyester or modi-fied vegetable oils with a sufficient hydroxyl number, ap-proximately in the range of 100 to 300. Castor oil with a hy-droxyl number of about 160 is suitable, as are usual glycols, in particular polyethylene glycols.
The monomer-reduced prepolymer itself is obtainable for example by removing the monomer in a thin-layer evaporator.
Alternatively or additionally one can react (residual) isocy-anate monomer with a hydroxy polyether and/or polyester and/or modified vegetable oil. Suitable vegetable oils are ones with a hydroxyl number of 100 to 300, for example castor oil with a hydroxyl number of about 160. According to the in-vention it is readily possible to obtain stable foams with such monomer-reduced prepolymer components, provided the polybutadiene is added. A prepolymer composition is termed low-monomer if it has less than 10% monomer, in particular less than 5% monomer; and substantially monomer-free if it 21~5877 has less than 2, preferably less than 1 and in particular less than 0.5 wt% monomer, always based on the prepolymer component, i.e. the reactive isocyanate-containing component present in the composition.
Suitable initial prepolymers for inventive foams, in particular 1.5C foams, have proved to be ones based on HDI, as offered for example by Bayer under the designations Desmo-dur DA and N 3400, as well as Desmodur N 3200 and N 3390.
These have a residual content of monomeric HDI of less than 0.5 wt%. Desmodur N is a dimeric HDI. These materials have not been applied in foam production up to now. Thcsc HDI
products can advantagcously The prepolymer can contain usual additives, for example polysiloxanes for controlling cell opening, flameproofing agents, softeners, catalysts, viscosity regulators such as propylene carbonate, triethyl phosphate and diphenylcresyl phosphate in quantities up to 40 wt%, based on the polymer component, dyes, rheology-controlling additives and the like.
The prepolymer composition, i.e. the PU prepolymer including all additives without propellants, expediently has an initial service viscosity at 20C of 5000 to 20000 mPa.s and prefera-bly of 8000 to 15000 mPa.s. According to the invention the content of NCO groups in the PU prepolymer is 4 to 20 wt%, preferably 6 to 18 wt% and in particular 7 to 13 wt%, based on the prepolymer.
Alternatively or additionally a tendency of linear foam systems to shrink can be counteracted by adding so-called cell openers. These are particularly paraffin oils with a density of 0.81 to 0.9 g/ml and a viscosity of 20 to 300 mPas/20C or silicone-free polymers based on polyvinyl alkyl ether with a foam-inhibiting effect, as are applied by BYK-Chemie GmbH under the designations Byk-051, -052 and -053 for lacquer systems. These additives are added in quantities of 0.01 to 2, preferably 0.1 to 1 wt%, based on the prepolymer component. It has surprisingly turned out that defoaming ad-ditives can actually counteract the tendency of polyurethane AMENDED SHEET

building foams to shrink.
Alternatively or additionally one can achieve a mechani-cal stabilization effect by incorporated mineral solids, for example by talcums, calcium carbonates, etc. In this case it is advantageous to use surface-active wetting additives to prevent signs of sedimentation. In combination therewith one can also use rheology-promoting additives, for example hydro-philic, colloidal silicic acid, as is available under the designation Aerosil.
The addition of a low quantity of polybutadiene makes it possible to increase the dimensional behavior of low-monomer and monomer-free PU prepolymers and obtain a fully foamable, dimensionally stable insulating material. Polybutadiene can be used in combination with PU prepolymers from all usual isocyanates, but is especially advantageous in combination with PU prepolymers based on HDI and MDI.
Suitable polybutadienes to be used are particularly liq-uid products as are offered by Huls AG with a viscosity of at least 500 mPa.s at 20C. Viscosity is preferably at least 2000 mPa.s at 20C and in particular about 3000 mPa.s at 20C. An especially suitable liquid polybutadiene is sold un-der the designation Polyol 130 with about 75% 1,4-cis double bonds, about 24% 1,4-trans double bonds and about 1% vinyl double bonds and a molecular weight (vapor-pressure osmotic) of about 3000. The content of liquid polybutadiene according to the invention is 0.01 to 2 wt% and preferably 0.05 to 1 wt%, based on the prepolymer component to which it is added.
Suitable polybutadienes are furthermore those products of higher molecular weight which can be added to the prepoly-mer composition in a dissolved form or be dissolved therein.
Also one can use higher-molecular polymeric hydrocarbons con-taining double bonds.
The molecular weight of suitable stabilizing additives is expediently 1000 to 9000, in particular up to 5000.
Along with pure (liquid) polybutadiene one can also use copolymers of l,3-butadiene with other 1,3-dienes, for exam-- 7 - 21~S877 ple isoprene, 2,3-dimethylbutadiene and piperylene, and with vinylaromatic compounds such as styrene, a-methylstyrene, vi-nyl toluene and divinylbenzene. The content of comonomers in the copolymers should not exceed 50 mol%. Such copolymers are regarded as falling within the designation "(liquid) polybu-tadiene" if they are liquid or soluble.
It is assumed that the dimensionally stabilizing effect of polybutadiene is based on its ability to crosslink in the presence of oxygen.
The inventive prepolymer composition contains in par-ticular propane, butane and/or dimethylether as a propellant component. Further propellants that can be used in the compo-nent are fluorocarbons which are liquefiable under the pres-sure conditions prevailing in a pressure tank, for example R 125, R 134a, R 143 and R 152a. To minimize the content of combustible and halogen-containing propellants one can add further gases which are not condensable under the pressure conditions prevailing in the pressure can, for example CO2, N2O or N2. CO2 is particularly preferred since it can partly dissolve in the prepolymer component and thereby contribute to foam formation, while also acting as a good propellant.
The propellant component of the prepolymer composition expediently constitutes 5 to 40 wt%. The CO2 content in the propellant can be for example about 5 wt%, based on the total propellant component. The content of gases not condensable under the prevailing pressure conditions should be such that the volume based on the empty space in the pressure tank yields a pressure of about 8 to 10 bars, depending on the relevant national specification for pressure tanks (aerosol cans). The empty space in the pressure tank is the space as-sumed by the uncondensed components of the prepolymer compo-sition.
The liquid butadiene is expediently added to the pre-polymer composition in solution along with an emulsifier -for example in a weight ratio of 80/20 -, preferably in solu-tion with a hydroxy vegetable oil suitable for controlling - 8 - 21~ S877 the isocyanate content of the PU prepolymer. It has proven especially suitable to use castor oil with a hydroxyl number of 160, but any other hydroxy vegetable oils and hydroxy polyethers and polyesters can also be used. These are hydroxy components as are conventionally used for modifying viscosity in the formulation of prepolymer compositions. The other di-mensionally stabilizing additives can be added accordingly.
The inventive prepolymer compositions can be used above all as 1.5C, but also as lC and 2C polyurethane foams. With 1.5C and 2C foams the polyol component required for curing the foam is kept separate from the prepolymer composition in known fashion and added only directly before or during dis-charge. The corresponding methods are widely described and known to the expert, as are suitable two-component pressure cans with a separate tank for the second component.
The second component can be in particular usual polyols, in particular glycol, glycerine and butanediol. To accelerate the curing reaction it may be expedient to add to this second component a usual catalyst, for example tin dioctoate, cobalt naphthenate and octoate, dibutyl tin dilaurate, metallic, in particular ferrous, acetonylacetate, DABCO crystalline and N-methyl-2-azanorbornane. Further catalysts are triethylenedi-amine, trimethylaminoethylpiperazine, pentamethyldiethylene-triamine, tetramethyliminobispropylamine, bis(dimethylamino-propyl)-N-isopropanolamine. It is also suitable to use het-eroaromatic amines, as stated for example in DF-A-42 15 647.
The invention relates further to the use of polyisocy-anate prepolymers based on hexamethylene-1,6-diisocyanates and its oligomerization products for producing prepolymer components for polyurethane insulating foams, in particular 1.5C foams, these HDI prepolymers being used alone or in com-bination with suitable other polyisocyanates, preferably ones based on biuret and TDI.
The inventive prepolymer compositions are suitable for insulating purposes. They have also proved particularly suit-able for producing spray adhesives, i.e. adhesives based on g polyurethane which can be sprayed from aerosol cans with the aid of air as an additional atomizing medium. These adhesives can be used advantageously for gluing insulating mats, also based on polyurethane, to each other and to a base.
The invention relates finally to the use of liquid poly-butadiene, paraffins and defoamers, as defined above, as an additive to isocyanate prepolymer compositions for polyure-thane insulating foams for controlling cell opening and di-mensional stability. The invention also relates to pressure cans for discharging polyurethane insulating foams with a prepolymer composition and optionally a separate polyol com-ponent, as described above.
Apart from the abovementioned dimensional stability of the inventive prepolymer composition produced with the addi-tion of liquid polybutadiene, the composition has the further advantage that it can be produced substantially free from chlorine and bromine and set to be fire-retardant without a need to add the usual halogen-containing flameproofing agents. This means that the addition of flameproofing agents for B2 foams according to DIN 4102 can be largely or fully dispensed with. This is the case in particular if the compo-sition contains phosphorus-containing thinners or softeners (viscosity regulators), for example triethyl phosphate. A
corresponding effect occurs with nitrogenous additives and vegetable oils, e.g. castor oil. If necessary, the prepolymer compositions can also be set to be substantially halogen-free, i.e. one can dispense not only with halogen-containing flameproofing agents but also with fluorocarbons as propel-lants. In this case it is sufficient for the propellant com-ponent to contain propane, butane, dimethylether and/or CO2.
It has turned out that these flame-retardant properties are due in particular to the trialkyl and triaryl phosphates and phosphonates. One can mention diphenylcresyl phosphate, triphenyl phosphate, triethyl phosphate, dimethylmethil phos-phonate and the like. One can further mention 2-ethylhexyl-diphenylphosphate and phosphoric acid-1,3-phenylenetetra-AMENDED SHEET

- 10- 21~5877 phenylester, which are commercially available under the des-ignations Pusflex 362 and Fyroflex RDP. Such phosphates and phosphonates can be present in the prepolymer composition in a quantity of 5 to 40 wt%, based on the prepolymer component.
They have the advantage that they do not disturb the balance of prepolymer, propellant and thinners in the prepolymer com-position but rather stabilize it, while conventional halogen-containing flameproofing agents interfere with this balance and can only be present with about 12 to 14 wt%.
The inventive prepolymer composition is produced in the fashion known in the art, whereby if low-monomer prepolymer is used it is put in the pressure tank as such or arises therein. One then adds to the prepolymer the liquid polybuta-diene, e.g. mixed with a surface-active agent and emulsified in a hydroxy oil, for example castor oil. The hydroxy oil or castor oil simultaneously serves to finely adjust the NCO
content of the prepolymer and lower the monomer content. Then the additives, such as flameproofing agents, stabilizers, softeners, catalysts, etc., are added, whereupon the pressure tank (aerosol can) is sealed and the propellant impressed.
The invention will be explained by the following exam-ples.

Example 1 Desmodur N 3400, an aliphatic polyisocyanate based on HDI with about 20 wt% NCO, is mixed in a protective atmos-phere with a polyol component. This polyol component consists of a polyesterol with a hydroxyl number of 239 (Ixol M 125 from Solvay) which simultaneously has flame-retardant proper-ties, a softener (trismonochlorisopropylphosphate, TMCP), a usual stabilizer (Tegostab B 1048) and catalysts (Texacat DMDEE, 2,2-dimorpholinodiethylether; Thancat DMP, dimethyl piperazine). The temperature is carefully controlled during addition.

AMENDED SHEET

The crosslinking agent used consists of monoethylene glycol to which an inductor (catalyst) is added.
With constant stirring the desired quantity of the above-described mixture is put in a moisture-free pressure tank which is sealed with a dome provided with a valve, with introduction of a cartridge having the second component (crosslinker). After sealing, a corresponding quantity of propellant is impressed. The individual components of the propellant mixture are expediently impressed successively and optionally filled up again in a second pass. An especially suitable mixture is of dimethylether in combination with one or more fluorocarbons (R 152a and R 134a).
In the following monomer-free prepolymer compositions and filling proportions for a pressure tank with a filling ratio of 75% are stated. The mixtures yield a dimensionally stable foam with good insulating properties. The content of residual monomer of the composition is under 0.5 wt%. The foam can also be used in particular as a spray adhesive.

Component Parts by weight ______________________________________________________ Castor oil 370 Softener (Levagard PP) 420 Flameproofing agent (Ixol M 125) 170 Stabilizer (Tegostab B 1048) 30 Texacat DMDEE 5 Thancat DMP 5 ______________________________________________________ Polyol component 1 1000 Polyol component 1 142 g Desmodur N 3400 181 g Propellant R 134a 30 g R 152a 60 g Dimethylether DME 10 g ______________________________________________________ Crosslinker: Monoethylene glycol 12 g Catalyst 5 g ______________________________________________________ Total 440 g Gas fraction (wt%) 23%

- - 12 _ 21~ S877 Examples 2 and 3 Inventive prepolymer compositions using conventional initial isocyanates were produced by the following recipes analogously to Example 1. The compositions yield an insulat-ing foam with good dimensional stability and good insulating properties. The content of residual monomer in the composi-tions is clearly under 0.5 wt%.
Desmophen N 75 designates a polyisocyanate with an NCO
content of 16.4 wt%, and Desmodur L 75 a polyisocyanate with an NCO content of 13 wt%. The former is a polyisocyanate con-taining biuret groups in 75% solution, the latter an addition polymer from TDI and TMP in 75% solution. Tego IMR 830 desig-nates a 10% emulsion of a liquid polybutadiene with a molecu-lar weight of about 3000 with a surface-active agent as an emulsifier (weight ratio 80/20; available from Goldschmidt) in castor oil with a hydroxyl number of 160.

Component Example 2 Example 3 Parts by weight Castor oil 320 320 Softener 420 420 Flameproofing agent (Ixol M 125) 170 170 Tego IMR 830 10% 50 50 Tegostab B 1048 30 30 (Stabilizer) Catalysts Texacat DMDEE 5 5 Thancat DMP 5 5 ____________________________________________________________ Polyol component 2/3 1000 1000 Polyol component 2/3 120 g 120 g Desmodur N 3400 150 g 150 g Desmodur N 75 50 g Desmodur L 75 50 g Propellant R 134a 30 g 30 g R 152a 60 g 60 g DME 10 g 10 g Crosslinker: Ethylene glycol 12 g 12 g Catalyst 5 g 5 g ___ _ _____________________________________________ Total 437 g 437 g Gas fraction (wt%) 23 23 . -13- 21SS877 Example 4 An inventive prepolymer composition was produced by the following recipe analogously to Example 1. The composition yields an insulating foam with good dimensional stability and good insulating properties. The content of residual monomer in the composition is under 0.5 wt%.

Component Parts by weight ______________________________________________________ Castor oil 320 Softener (Levagard PP)370 Solvent (propylene carbonate) 60 Flameproofing agent (Ixol M 125)170 Tego IMR 830 (10%) 50 ~Cell regulator) Stabilizer (Tegostab B 1048) 30 Catalysts Texacat DMDEE 5 Thancat DMP 5 ___________________________ __________________________ Polyol component 4 1000 Polyol component 4 110 g Desmodur N 75 50 g Desmodur N 3400 150 g Propellant R 134a 30 g R 152a 60 g DME 10 g ______________________________________________________ Crosslinker: Ethylene glycol 13 g Catalyst (Thancat AN 10, Fe-acetonylacetate) 4 g Total 427 g Gas fraction (wt%) 23 Examples 5 and 6 Inventive prepolymer compositions were produced by the following recipes analogously to Example 1. The compositions yield an insulating foam with good dimensional stability and good insulating properties. The content of residual monomer is under 0.5 wt%.

AMENDED SHEET

Components Example 5 Example 6 ____________________________________________________________ Polyol component 2/3 110 g 110 g Desmodur N 3400 100 g 100 g Desmodur DA 100 g 100 g Propellant R 134a 30 g 30 g R 152a 60 g 60 g DME 10 g 10 g Crosslinker Ethylene glycol13 g 13 g Catalyst 4 g 4 g (Thaneat AN 10, Dabco T-9) __________________________________________ Total 427 g 427 g Examples 7 and 8 Inventive prepolymer compositions were produced by the following recipes analogously to Example 1. The compositions yield an insulating foam with good dimensional stability and good insulating properties. The content of residual monomer in the composition is under 0.5 wt%.
The composition contains an extending mineral for pro-moting dimensional stability in the form of talcum (Finntalc M-15) or calcium carbonate (Ultracarb U-5).

AMENDED SHEET

Components Example 7 Example 8 ____________________________________________________________ Castor oil 320 320 Softener 325 325 Flameproofing agent 150 150 Tego IMR 830 (10~) 50 50 Wetting additive (Byk 160) 5 5 Thixotroping agent (Aerosil 200) 10 10 Extending mineral Finntalc M-15 100 Ultracarb U-5 100 Tegostab B 1048 30 30 Texacat DMDEE 5 5 Thancat DMP 5 5 Polyol component 7/8 1000 1000 Polyol component 7/8 142 g 142 g Desmodur N 3400 181 g 181 g Propellant R 134a 30 g 30 g R 152a 60 g 60 g DME 10 g 10 g Crosslinker: Ethylene glycol12 g 12 g Catalyst 5 g 5 g _________________________________________ _ Total 440 g 440 g NCO surplus (wt~) 4.01 4.01 The designations "Desmodur", "Tego", "Aerosil", "Finntalc", "Ultraearl", "Tegostab", "Texacat", "Thancat", "Levagard" and "Ixol" are trademarks.

AMENDED SHEET

Claims

1. A prepolymer composition for producing polyurethane insulating foams from pressure tanks which consists of a pre-polymer component with at least one PU prepolymer with a con-tent of NCO groups of 4 to 20 wt% and usual additives, as well as a propellant component, characterized by the use of a PU prepolymer based on hexamethylene-1,6-diisocyanate alone or mixed with other polyisocyanates, the content of monomeric isocyanate being less than 2 wt%, based on the prepolymer component.

2. The prepolymer composition of claim 1, characterized by a PU prepolymer based on aliphatic and aromatic polyisocy-anates and polyetherols.

3. The prepolymer composition of claim 2, characterized in that the polyisocyanate is one based on hexamethylene-1,6-diisocyanate, naphthalene-1,5-diisocyanate, tolylene diisocy-anate, isophorone diisocyanate or diphenylmethane diisocya-nate.

4. The prepolymer composition of any of the above claims, characterized by a content of liquid polybutadiene of 0.02 to 1 wt%.

5. The prepolymer composition of claim 4, characterized in that the liquid polybutadiene contains about 75% 1,4-cis double bonds, about 24% 1,4-trans double bonds and about 1%
vinyl double bonds, has a molecular weight, determined by va-por-pressure osmosis, of about 3000 and a viscosity at 20°C
of about 3000 mPa.s.

6. The prepolymer composition of any of the above claims, characterized by a content of paraffin oil or de-foamer of 0.01 to 2 wt%, based on the prepolymer component.

7. The prepolymer composition of any of the above claims, characterized by a propellant content of 5 to 40 wt%.

8. The prepolymer composition of any of the above claims, characterized in that the propellant component con-tains propane, butane and/or dimethylether.

9. The prepolymer composition of any of the above claims, characterized in that the propellant component con-tains fluorocarbon, in particular R 125, R 134a, R 143 and/or R 152a.

10. The prepolymer composition of any of the above claims, characterized by an initial service viscosity of the PU prepolymer at 20°C of 5000 to 20000 mPa.s.

11. The prepolymer composition of claim 11, character-ized by an initial service viscosity of the PU prepolymer of 8000 to 15000 mPa.s.

12. Use of polyisocyanate prepolymers based on hexa-methylene-1,6-diisocyanate for producing the prepolymer com-positions of any of the above claims.

13. The use of claim 12, characterized in that the pre-polymer compositions is intended for producing 1.5C polyure-thane insulating foams.

14. Use of the prepolymer composition of any of claims 1 to 11 for producing spray adhesives based on polyurethane.

15. A pressure can for discharging 1C polyurethane insu-lating foams, characterized in that it contains a prepolymer composition of any of claims 1 to 11.