ZA200207411B

ZA200207411B - Polyurethane foams with reduced exothermy.

Info

Publication number: ZA200207411B
Application number: ZA200207411A
Authority: ZA
Inventors: Theodore Frick; Ernest-Martin Hoppe; Manfred Kapps; Frank Meyer
Original assignee: Bayer Ag; Carbotech Fosroc Gmbh
Priority date: 2000-04-13
Filing date: 2002-09-16
Publication date: 2003-09-16
Also published as: UA73564C2; CN1422292A; PL206612B1; WO2001079321A1; DE10018395A1; DE10018395B4; AU6017501A; PL358663A1; HK1054559B; CN1167723C; HK1054559A1; AU2001260175B2

Description

Polyurethane foams of low exothermicity

The invention relates to polyurethane foam systems of low exothermicity and to their use for consolidating geological formations in underground mining, in tunnel construction and in civil engineering.

Two-component polyurethane foam systems are employed to a large extent in underground coal mining for consolidation of rock and coal and for sealing off against inflowing waters. The formation of polyurethane from polyisocyanates and polyols is exothermic in principle. Under adverse circumstances ignition of coal dust may occur as a consequence of the high reaction temperatures which arise in the foamed body. When the reaction mixture flows in to relatively large hollow spaces in particular, the core temperature of the polyurethane foam can increase to such an extent that self-ignition of the polyurethane and consequently burning of coal in situ can occur.

To avoid this disadvantage of polyurethane systems, EP-A 167 002 proposed the use of reaction products of isocyanates with aqueous alkali metal silicate solutions. EP-

A 636 154 discloses ..... by reaction of polyisocyanates, aqueous alkali metal silicate solutions and cement. However, these systems have not found acceptance in practice.

It has now been found that by combination of certain polyisocyanate prepolymers with selected polyols and suitable fillers, the exothermicity of the polyurethane formation can be lowered to the extent that risk of fire no longer occurs during consolidation of rock.

The invention therefore relates to foams which contain polyurethane groups and are obtained by reaction of

1. a polyisocyanate component with an NCO content of 20 to 30 wt.%, preferably 23 to 28 wt.%, which comprises at least 50 wt.% of a prepolymer containing isocyanate groups with an NCO content of 20 to 28 wt.%, 2. a polyol component with an OH number of 120 to 350, preferably 180 to 300, 3. a solid filler which is dispersed in the polyol component b) or the prepolymer a), preferably in the polyol component b), and has an average particle size of 4 to 100 um, preferably 4 to 25 pm, in particular 10 to 25 um, 4, water, 5. optionally catalysts, 6. optionally additional additives.

According to the invention, the isocyanate component a) contains 20 to 30 wt.%, preferably 23 to 28 wt.%, of NCO groups and comprises at least 50 wt.% of a prepolymer containing 20 to 30 wt.%, preferably 23 to 28 wt.%, of isocyanate groups. This prepolymer is preferably prepared by reaction of isocyanates of the diphenylmethane series with polyether polyols with a functionality of 3 to 8 and an

OH number of 350 to 1,000 and a number-average molecular weight of 150 to 1,000. Suitable prepolymers are also described in EP-A 550 901. Isocyanates of the diphenylmethane series which are employed are di-nuclear diphenylmethane- diisocyanates, such as 4,4'- and/or 2,4'-diphenylmethane-diisocyanate or higher homologues thereof or mixtures of diphenylmethane-diisocyanates with two or more nuclei, for example polyphenylene-polymethylene-polyisocyanates, such as are prepared by aniline-formaldehyde condensation and subsequent phosgenation ("crude MDI") or the polyisocyanates with a functionality higher than 2.0 which are obtainable industrially under the name "polymeric diphenylmethane-diisocyanate",

Products which comprise 75 to 95 wt.% of di-nuclear isomers are preferred, in particular those in which the content of the 2,4"-isomer in the di-nuclear isomers is 15 to 40 wt.% and the content of 2,2'-isomer is 2 to 10 wt.%.

In addition to the prepolymer, the isocyanate component a) can comprise up to 50 wt.% of further isocyanates of the diphenylmethane series. This is preferably polymeric MDI. However, monomeric MDI can also be employed, or MDI types which are modified, e.g. contain biuret, allophanate or isocyanurate groups, as long as the viscosity of the isocyanate component a) does not thereby rise too much.

To ensure a good processability of the isocyanate component a), its viscosity is preferably established in a range from 200 to 6,000 mPas, particularly preferably 500 to 3,000 mPas. Such isocyanate components can be conveyed and injected into the rock mass formations without problems using the piston or gear pumps conventionally used for consolidating rock mass.

The polyol component b) has an OH number of 120 to 350, preferably 180 to 300.

The polyol component preferably comprises polyoxyalkylene polyols which have functionalities of 2 to 8, preferably of 2 to 4, and are obtained by polyaddition of alkylene oxides, such as, for example, ethylene oxide, propylene oxide, butylene oxide, decyloxirane or phenyloxirane, preferably ethylene oxide and/or propylene oxide, on to starter compounds with active hydrogen atoms. Starter compounds which are employed are compounds with two or more hydroxyl end groups, such as, for example, water, triethanolamine, 1,2-ethanediol, 1,2-propanediol, 1,3- propanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-hexanediol, 1,3- hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, glycerol, trimethylolpropane, pentaerythritol or sorbitol. The starter compounds can be used by themselves or as mixtures.

One or more polyester polyols can also be co-used in the polyol component b) in amounts of up to 10 wt.% of the total amount of component b). Suitable polyester polyols have number-average molecular weights of 200 to 6,000 g/mol, preferably 200 to 2,400 g/mol, and are obtainable from aromatic and/or aliphatic dicarboxylic acids and polyols which contain at least two hydroxyl groups. Examples of dicarboxylic acids are phthalic acid, isophthalic acid, terephthalic acid, fumaric acid, maleic acid, azelaic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, malonic acid and succinic acid. The pure dicarboxylic acids and any desired mixtures thereof can be used. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives, such as e.g. dicarboxylic acid mono- or diesters of alcohols having one to four carbon atoms, can also be employed. Such esters are formed, for example, in the recycling of polyester waste. Dicarboxylic acid anhydrides, such as phthalic anhydride or maleic anhydride, can also be employed as the acid component. The following are preferably used as the alcohol component for the esterification: ethylene glycol, diethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6- hexanediol, 1,10-decanediol, glycerol, trimethylolpropane, pentaerythritol or mixtures thereof. It is also possible to use polyester polyols from lactones, e.g. e- caprolactone, or hydroxycarboxylic acids, e.g. w-hydroxycarboxylic acids. The polyol component can also comprise polyether-ester polyols, such as are obtainable e.g. by reaction of phthalic anhydride with diethylene glycol and subsequent reaction with oxirane.

In the preparation of the foams according to the invention, a solid filler with an average particle size of 4 to 100 um, preferably 4 to 25 pm, in particular 10 to 25 pm, is employed as component c). Storage-stable dispersions with a viscosity suitable for processing can be obtained with such fillers. Suitable fillers are, for example, aluminium trihydroxide, urea-formaldehyde resins (condensation products of urea and formaldehyde, sce Houben-Weyl, "Methoden der organischen Chemie", vol. XIV, 1963, p. 319-402), rock powder or pyrogenic silica; aluminium trihydroxide is preferred. For the preparation of the foams according to the invention, the filler is dispersed or suspended in the polyol component b) or the prepolymer a), preferably in the polyol component b). The filler is preferably employed in an amount of 30 to 55 wt.%, particularly preferably 35 to 50 wt.%, based on the amount of the suspending agent.

If the filler is dispersed in the polyol component b), the viscosity of the filler- containing polyol component should preferably be not more than 6,000 mPas, so that it can be conveyed via a low-pressure pump. The viscosities of the isocyanate component and filler-containing polyol component are particularly preferably adjusted to approximately the same value, in order to facilitate processing, in particular uniform mixing of the components.

For the preparation of the foams according to the invention, water is added as the blowing agent d), preferably in an amount of 0.1 to 1 wt.%, particularly preferably 0.6 to 0.9 wt.%, based on the polyol component b). The amount of water is very particularly preferably chosen such that a foaming factor of 2 to 6 is achieved, i.e. the volume of the foam prepared is two to six times the total volume of the starting components.

Catalysts e) which accelerate the reaction between the isocyanate component and the polyol component can optionally be added during the preparation of the foams according to the invention. Examples of suitable catalysts are organotin compounds, such as tin(Il) salts of organic carboxylic acids, e.g. tin(Il) acetate, tin(II) octoate, tin(Il) ethylhexoate and tin(I) laurate, and the dialkyltin(IV) salts, e.g. dibutyltin diacetate, dibutyltin dilaurate and dioctyltin diacetate. Further examples of suitable catalysts are amines, such as dimethylaminopropylurea, dimethylaminopropylamine, bis(dimethylaminopropyl)amine, diazabicyclooctane, dimethylethanolamine, triethylamine, dimethylcyclohexylamine, dimethylbenzylamine, pentamethyldiethylenetriamine, N,N,N'N'-tetramethylbutanediamine, N- methylmorpholine, bis(dimethylaminoethyl) ether and tris(dialkylaminoalkyl) -s- hexahydrotriazines.

Examples of suitable catalysts for producing polyisocyanurate structures are potassium salts, such as potassium acetate or potassium octoate. A combination of several catalysts can also be used.

Further additives f) are optionally also used for the preparation of the foams according to the invention, for example pigments, dyestuffs or plasticizers, such as dioctyl phthalate. These are usually added to the polyol component in amounts of 0 to 10 parts by weight, preferably 0 to 5 parts by weight.

Flameproofing agents are optionally also added, preferably those which are liquid and/or soluble in one or more of the components employed for the preparation of the foam. Commercially available phosphorus-containing flameproofing agents are preferably employed, for example tricresyl phosphate, tris-(2-chloropropyl) phosphate, tris-(2,3-dibromopropyl) phosphate, tris-(1,3-dichloropropyl) phosphate, tetrakis-(2-chloroethyl)ethylene diphosphate, diethylethane phosphonate and diethanolaminomethylphosphonic acid diethyl ester. Halogen- and/or phosphorus- containing polyols which have a flameproofing action are also suitable. The flameproofing agents are preferably employed in an amount of not more than 35 wt.%, particularly preferably not more than 20 wt.%, based on component b).

The invention also provides the use of the foams according to the invention for consolidation of rock in mining and civil engineering, for example for consolidation of coal and surrounding rock, and for sealing off against inflowing waters in underground hard coal mining.

Due to geological fault zones and the hollow spaces caused by extraction, outbursts of rock from the hanging sides are forever occurring, leading to serious interruptions in production and to a considerable danger to the persons working underground.

During consolidation of the rock mass, the polyurethane foams according to the invention are forced via bore holes by means of suitable injection pumps into the rock mass formation to be consolidated. The expanding reaction mixture cements the filled gaps and cracks and thus leads to a re-establishment of the system strength of the geological formation; caving in of rock or of coal is reliably prevented.

The preparation of the foams according to the invention is preferably carried out by mixing, in a volume ratio of 1:1, the isocyanate component a) and a mixture comprising components b), c), d), €) and f). An NCO/OH ratio of 130 to 300 is preferably established here, particularly preferably 180 to 260.

The recipe for the foams according to the invention is preferably chosen such that the temperature which the reaction mixture reaches during the polyurethane formation does not exceed a maximum of 120°C. Recipes in which the maximum reaction temperature does not exceed 110°C are particularly preferred.

Claims

Patent claims

1. Foams containing polyurethane groups, obtainable by reaction of a) a polyisocyanate component with an NCO content of 20 to 30 wt.% which comprises at least 50 wt.% of a prepolymer containing isocyanate groups with an NCO content of 20 to 28 wt.%, b) a polyol component with an OH number of 120 to 350, c) a solid filler which is dispersed in the polyol component b) or the prepolymer a) and has an average particle size of 4 to 100 um, d) water, e) optionally catalysts, f) optionally additional additives.

2. Process for the preparation of foams according to claim 1 containing polyurethane groups, in which the isocyanate component a) is reacted in a volume ratio of 1:1 with a mixture comprising components b), c), d) and optionally €) and f).

3. Use of the foams according to claim 1 for consolidation of rock in mining and civil engineering.