GB2094322A - Manufacture of rigid polyurethane foams from polyether- polyols and polyhydroxypolyphenylalkanes - Google Patents

Abstract

Rigid polyurethane foams are obtained from a polyetherpolyol, a polyisocyanate, a blowing agent and a polyhydroxypolyphenylalkane in particular bis-(p-hydroxyphenyl)- methane or 2,2-bis-(-p- hydroxyphenyl)-propane, the polyhydroxypolyphenylalkane/ polyether polyol weight ratio being at most 1/2. Solutions of the polyhydroxypolyphenylalkane in the polyether polyol in the above weight ratio are also described. The foams possess an increased resistance to crushing forces.

Description

SPECIFICATION Manufacture of rigid polyurethane foams from polyether-polyols and polyhydroxypolyphenylalkanes This invention relates to a process for the manufacture of bodies of rigid polyurethane foam possessing improved mechanical properties.

It is known to manufacture bodies of rigid polyurethane foam from reactive compositions for making polyurethane, containing one or more polyether-polyols, one or more organic polyisocyanates and also various additives such as catalysts, blowing agents, fire-proofing agents and surface active agents. The polyether-polyols commonly used for this purpose are compounds resulting from the polyaddition of propylene oxide to polyhydroxyl compounds containing at least three hydroxyl groups per molecule, such as sucrose, their hydroxyl number being most frequently of the order of 350 to 500.

The bodies of rigid polyurethane foam thus obtained possess satisfactory mechanical properties in applications where they are not subjected to relatively large crushing forces. However, in certain applications, such as the insulation of floors of industrial buildings or of refrigerator lorries, it is desirable to obtain bodies of polyurethane foam possessing an increased resistance to crushing forces.

It is known to introduce, into the above-mentioned reactive compositions for making polyurethane, crosslinking agents which are aliphatic compounds having a molecular weight of less than 300 and containing several hydroxyl and/or amine groups per molecule. The compounds of this type which are most commonly used are glycerol, sorbitol, ethylene glycol, triethanolamine, ethylenediamine and diethylenetriamine or compounds obtained by the polyaddition of propylene oxide and/or ethylene oxide to the above hydroxyl and/or amino compounds. These crosslinking agents, the hydroxyl number of which is commonly between 700 and 1,800, are used in proportions of the order of 5 to 10% by weight of all the compounds reacting with the organic polyisocyanates.

These crosslinking agents lead to bodies of rigid polyurethane foam, the crushing strength of which is slightly higher, but they have various disadvantages; in particular they result in a greatly increased consumption of organic polyisocyanates. Hydroxyl crosslinking agents are by nature very reactive towards isocyanate groups, and amino crosslinking agents strongly catalyse the formation of polyurethanes; thus, the reactive compositions for making polyurethane in which these crosslinking agents are present can easily lead to phenomena of excessively rapid setting, and this results in poor filling of the volumes to be filled or in stretching at the end of expansion, which causes a marked reduction in the mechanical strength in the directions perpendicular to the direction of the expansion.

This reduction can cause the spontaneous deformation of these foams.

It has now been found, according to the present invention, that the addition of polyaromatic polyhydroxyl compounds, such as dihydroxydiphenylalkanes, makes it possible to obtain bodies of rigid polyurethane foam possessing improved mechanical properties, without, on the other hand, having the abovementioned disadvantages. On the contrary, it has been observed that the use of the reactive compositions for making polyurethane, according to the invention, is facilitated because the reactions which lead to the formation of the foams are more gradual and the filling of the moulds is improved.

Furthermore, the so-called "core scorching" and cracking phenomena do not normally occur, even in bodies of large dimensions (for example 3 m x 1 m x 1 m) and even if the bodies have a relatively high density (for example of more than 60 kg/m3).

The invention thus provides a process for the manufacture of bodies of rigid polyurethane foam from a reactive composition for making polyurethane, comprising polyether-polyols, blowing agents and organic polyisocyanates, these compositions also containing one or more polyhydroxypolyphenylalkanes in an amount such that the weight ratio polyhydroxypolyphenylalkane/polyether-polyol is equal to at most 1/2 and preferably 1/10 to 1/3.

The polyhydroxypolyphenylalkanes used are compounds containing at least two aromatic nuclei and two hydroxyl groups attached directly to the aromatic nuclei, the aromatic nuclei themselves being joined by an aliphatic radical having from, say, 1 to 3 carbon atoms.

Amongst the polyhydroxypolyphenylalkanes, the compounds comprising two to five aromatic nuclei and one OH group per nucleus, and more particularly bis-(p-hydroxyphenyl)-methane and 2,2-bis (p-hydroxyphenyl)-propane, are preferred. Compounds of this type can be obtained by condensing two molecules of phenol with one molecule of formaldehyde or isopropanone.

The polyether-polyols used can be chosen from those polyether-polyols used in the manufacture of rigid polyurethane foams. These polyether-polyols generally have a hydroxyl number of 300 to 1,000 and preferably 350 to 500. They can be prepared in known manner by the polyaddition of propylene oxide, and if appropriate ethylene oxide, to compounds containing mobile hydrogen atoms, such as polyols, oses, giucosides, alkanolamines or polyamides, it being possible for these compounds to possess, according to the particular case, from 2 to 8 hydrogen atoms capable of reacting with the alkylene oxides. The polyaddition is most frequently carried out in the presence of an alkaline compound, such as potassium hydroxide, until the desired amount of the alkylene oxide or oxides has been added.The alkaline compound is then removed, for example by neutralising this compound with an acid and then filtering off the salt formed.

If the polyether-polyols are prepared from ethylene oxide and propylene oxide, these alkylene oxides can be attached separately or in a mixture to the compounds containing mobile hydrogen atoms, or by altering these two methods of attachment. The chosen method of attachment influences the reactivity of the polyether-polyols towards the polyisocyanates.

In the compositions used according to the present process, the polyether-polyol and the polyhydroxypolyphenylalkane and their respective amounts should be chosen, within the limits given above, so that the polyether-polyol provides more than 50%, and preferably from 60 to 90%, of the hydroxyl groups provided by the polether-polyol/polyhydroxypolyphenylalkane combination.

The organic polyisocyanates are advantageously chosen from amongst aromatic polyisocyanates such as tolylene diisocyanate, commonly referred to as "TDI", or 4,4'-diphenylmethane diisocyanate, commonly referred to as "MDI". These organic polyisocyanates are preferably chosen from crude aromatic polyisocyanates, such as crude TDI products, which are obtained by reacting phosgene with a crude tolylenediamine containing various isomers and condensed amines, or crude MDI products, which result from the condensation of phosgene with the unpurified product from the reaction of aniline with formaldehyde. The organic polyisocyanates are generally used in amounts such that the isocyanate number is 1.00 to 3.50 and preferably 1.05 to 1.1 5.

The isocyanate number mentioned above is equal to the ratio of the number of isocyanate groups in the organic polyisocyanates to the number of mobile hydrogen atoms in the polyether-polyols, the polyhydroxypolyphenylalkanes and, if appropriate, the water used as a blowing agent.

The blowing agents are generally volatile organic compounds such as monofluorotrichloromethane or methylene chloride. These volatile organic compounds are suitably used in amounts of up to 30% by weight of the polyetherpolyols. Small amounts of water, for example about 0.5% by weight, relative to all the polyether-polyols and the polyhydroxypolyphenylalkanes, can also be used as a complementary blowing agent.

If the foaming mixture contains polyether-polyols prepared from amino compounds, it is not generally necessary to use catalysts, because these polyether-polyols possess a high reactivity towards the organic polyisocyanates. If the reactivity of the foaming mixture towards the polyisocyanates is inadequate, it may be helpful to use catalysts, in particular amino catalysts and especially tertiary amines such as triethylenediamine, dimethylethanolamine, triethylamine, triethanolamine, dimethylcyclohexylamine or mixtures of these amines. These catalysts are generally used in amounts which are less than 3% by weight, relative to all the polyhydroxyl compounds.Although it is not essential, it is possible to combine these amino catalysts with metal catalysts such as stannous octoate, dibutyl-tin dilaurate or zinc octoate, in particular in order to increase the reaction rate of the constituents of the reaction mixture.

It is generally helpful also to introduce, into the foaming mixture, emulsifiers such as silicone emulsifiers resulting from the condensation of alkylene oxides with silanes or with siloxanes. These emulsifiers are generally used in proportions of 0.3 to 1% by weight, relative to the foaming mixture.

In order to increase the self-extinguishability properties of the bodies of rigid polyurethane foam obtained, it is possible to add, to the reactive compositions, fireproofing compounds which are inert or reactive towards the organic polyisocyanates, such as tris-chloroethyl phosphate, tris-chloropropyl phosphate, tri-(dibromopropyl) phosphate, antimony oxide, red phosphorus, or phosphorus compounds or phosphochlorinated compounds such as the products sold commercially under the names Phosgard C 22 R, Fyrol 6 and Napiol R 104. These fireproofing compounds are generally used in proportions of 2 to 7% by weight, relative to the reactive compositions.

The process of the invention can be carried out by mixing the constituents of the reaction composition for making polyurethane, the organic polyisocyanates preferably being introduced last. It is convenient to use the polyhydroxypolyphenylalkanes in solution, for example in the polyether-polyols.

The solutions of these polyhydroxyl compounds in the polyether-polyols represent a further aspect of the present invention.

The process of the invention can be carried out on an industrial scale by moulding, using a machine with several circuits terminating at a mixing head, one of the circuits making it possible to introduce the polyisocyanates separately into the mixing head. The constituents of the reactive compositions are generally used at a temperature of 200 to 300 C. The foaming mixture is cast into a mould, which is itself at a temperature determined according to the moulding conditions and is 200 to 700C, in amounts such that the average density of the moulding is 30 to 800 kg/m3 and preferably 30 to 150 kg/m3. The mould is then closed for a few minutes to allow the foam to expand and polymerise.

The mouldings obtained according to the process of the invention possess valuable mechanical properties, as demonstrated by the following Examples which further illustrate the present invention.

For an essentially equal density, the mouldings have, in particular, a markedly increased so-called "parallel" crushing strength, an improved so-called "perpendicular" crushing strength and better dimensional stability.

EXAMPLE 1 AND COMPARISON EXAMPLES C, and C2 Reactive compositions for making polyurethane are prepared from the constituents shown in Table 1. it is observed that the cream time of the compositions according to the invention is shorter than that of the compositions of Examples C1 and C2, whereas the thread-drawing time is essentially the same.

Whereas the foams of Examples 1 and of Comparison Examples C, and C2 have essentially the same density, it is found that the foam prepared according to the invention has a very markedly increased "parallel" crushing strength and also a substantially improved "perpendicular" crushing strength and substantially improved dimensional stability. The values preceded by the sign + indicate the scatter of the measurements obtained on different samples taken from one and the same block of foam. It is observed that the mechanical properties are more homogeneous in the case of the foams obtained according to the invention than in the case of the foams of the comparison examples.

In the table, the references (1), (2) and (3) have the following meanings: (1) = Compound resulting from the polyaddition of propylene oxide to sucrose in solution, having a hydroxyl number of 410 and an average number of functional groups of 2.5 to 3 (OH groups per molecule) (2) = AFNOR Standard Specification NFT 56 101 (3) = AFNOR Standard Specification NFT 56 122

Example 1 Example C1 Example C2 Polyether-polyol (1) 72 (75)* 90 85 2,2-bi s-(p-hydroxypheny l)-propane 18 (25)* 0 0 Glycerol 0 0 5 Tri-(chloropropyl) phosphate 10 10 10 H20 0.5 0.5 0.5 Silicone 1.2 1.2 1.2 Dimethylcyclohexylamine 0.5 1.2 1.2 Monofluorotrich loromethane 31 28 32 Crude MDI 107 103 121 Isocyanate number 106 106 106 Cream time 35 seconds 55 seconds 45 seconds Thread-drawing time 3 minutes 3 minutes 3 minutes 25 seconds 20 seconds 15 seconds Density, kg/m3 (D) 30.3 +0.4 31.3 + 1.3 30.5 + 1,2 Crushing strength (CS):: Parallel CS (2) (kPa) (CS / /) 297 + 9 227 + 20 240 +30 Perpendicular CS (2) (kPa) (CSl) 113 +6 108+12 90j11 Ratio: CS// x 10 97.8 72.5 78.6 D Ratio: CS#x 10 D Dimensional stability (3) (#V/V %) - 24 C 0.6 # 0.3 1.0 # 0.3 1 # 0.3 + 70 C 100% relative humidity 10 # 2.2 15 # 3.6 13 # 3 + 80 C 2.2 # 0.3 3.2 # 1.1 3 # 1.2 *The values (75) and (25) are the percentages of OH groups provided respectively by the poly ether-polyol and by the 22-b s-(p-hydroxy-pheny 1)-propane.

Claims (16)

1. Process for the manufacture of a body of a rigid polyurethane foam which comprises allowing a reactive composition comprising at least one polyether-polyol, blowing agent and organic polyisocyanate, as well as one or more polyhydroxypoiyphenylalkanes which contain at least two aromatic nuclei and at least two hydroxyl groups attached directly to the aromatic nuclei, the said nuclei being joined to one another by an aliphatic radical containing 1 to 3 carbon atoms, in an amount such that the weight ratio polyhydroxypolyphenylalkane/polyether-polyol is equal to at most 1/2 to react and foam.

2. Process according to claim 1 in which the said weight ratio is 1/10 to 1/3.

3. Process according to claim 1 or 2 in which the polyether-polyol is used in an amount such that it provides more than 50% of the OH groups provided by the polyether-polyol/ polyhydroxypolyphenylalkane combination.

4. Process according to claim 3 in which the polyether-polyol provides 60 to 90% of the OH groups provided by the said combination.

5. Process according to claim 1 in which the polyhydroxypolyphenylalkane is bis-(phydroxyphenyl)-methane or 2,2-bis-(p-hydroxy-phenyl)-propane.

6. Process according to any one of the preceding claims in which the polether-polyol has a hydroxyl number of 300 to 1,000, and results from the polyaddition of propylene oxide, and, optionally, ethylene oxide, to compounds containing from 2 to 8 mobile hydrogen atoms.

7. Process according to claim 6 in which the polyether-polyol has a hydroxyl number of 350 to 500.

8. Process according to any one of the preceding claims in which the polyhydroxypolyphenylalkane is incorporated in the composition as a solution in the polyether-polyol.

9. Process according to any one of the preceding claims in which the organic polyisocyanate is a crude tolylene diisocyanate or crude 4,4'-diphenylmethane diisocyanate.

10. Process according to any one of the preceding claims in which the isocyanate number is 1.00 to 3.50.

11. Process according to claim 10 in which the isocyanate number is 1.05 to 1.15.

12. Process according to any one of the preceding claims for the production of a moulded body having an average density of 30 to 800 kg/m3.

1 3. Process according to claim 1 substantially as hereinbefore described.

14. A body of rigid polyurethane foam whenever manufactured by a process as claimed in any one of the preceding claims.

1 5. A solution of polyhydroxypolyphenylalkane which contains at least two aromatic nuclei and at least two hydroxyl groups attached directly to the aromatic nuclei, the said nuclei being joined to one another by an aliphatic radical containing 1 to 3 carbon atoms, in a polyether-polyol, the weight ratio of the polyhydroxypolyphenylalkane/polyether-polyol being at most 1/2.

16. A solution according to claim 15 which.has one or more of the features of claims 2 to 8.