CA1051600A - Process for the preparation of polyurethane foam - Google Patents

Abstract

A PROCESS FOR THE PREPARATION
OF POLYURETHANE FOAM

ABSTRACT OF THE DISCLOSURE

A process is provided for the preparation of soft hydrophilic polyurethane foam using a polyether polyol mixture having a high proportion of primary alcohol groups and a selected ratio of polyisocyanate to polyol.

Description

L6~1 SPECIFICATION
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The degree of hardness is one basis of classification of polyurethane foams, and one usually distinguishes between flexible foam, semi-rigid foam, and rigid foam. The hydroxyl content or number of the polyether polyol used principally determines the degree of hardness. A
step forward in the development of polyurethane foam less hard or softer than what is re-Eerred to as flexible foam is the so-called supersoft foam, obtained by reacting a polyisocyanate with a polyol of suitable properties in a weight ratio such that the isocyanate index, i. e. the ratio between isocyanate groups and hydroxyl ~roups present in the reaction mixture, does not e}~ceed 1. 0. Also, certain softening agents and blowing a~ents may in some cases decrease the hardness of the foam.
Hypersoft; polyurethane foams (i. e. foams of very low hardness) have been prepared by the process disclosed in French patent - 15 No. 2,172,860, using a mixture of two mutually insoluble polyethel polyols, in which case the mixture of the t~vo polyols must conform to the following specifications:
(a) The mixture of polyether polyols contains from 50 to 70~C
by weight of oxyethylene units, i. e., units derived from ethylene oxide;
(b) The proportion of primary hydroxyl groups compared to the total amount of hydro~yl groups is from 35 to 50~c;
(c) The ratio between the percenta~e by weight OI oxyethylene units, i. e. units derived from ethylene oxide,according to ~a~ and the - percentage of primary hydro~Yyl groups according to ~) is from 1.1 to 1. 7.
These so~t foarns have a considerably lower degree of hardness, '`'' ' ' 35~6~

i. e. a~e softer, than the pre~iously mentioned supersoft foams. This is why this category of foam is usually designated hypersoft.
In accordance with the present invention, polyurethane foams softer than hypersoft foams~ i. e. of still lower hardness than those poly-5 urethane foams prepared according to the process of French patent No.2,172, 860, are obtained by using a polyether polyol mixture containing an unusu~lly high proportion of primary hydroxyl groups, within a carefully selected ratio of the amount of polyisocyanate to polyol. More particularly~
the present invention prwides a process Eor the preparation oP super-lQ hypersoft polyurethane foam, of a low degree of hardness, that is alsohighly hydrophilic,by reacting polyisocyanate with a polyether polyol mixture of at least two mutually insoluble poly~mctional polyether polyols containing from about 50 to about 70~/c by weight oxyethylene units (derived from ethylene oxide) in the presence of catalyst, blowing agent, foam 15 stabili~er and, if desired, any other additives commonly used in the preparation of polyurethane foam. The terni "polyfunctional" as used herein refers to triEunctional alld higher, and excludes mono and bifunctional.
The polyether poly~l mixture used in the process of the irlvention has a hydroxyl number of from 35 to 45, and from 55 to 80~
20 primary hydroxyl groups of the total number of hydroxyl groups in the polyether polyol mixture. The amounts oF polyisocyanate and polyether polyol are selected so that the ratio of isocyanate groups to hydroxyl groups is from 0. 85 to 1. 05, preferably from 0. 90 to 0. 98.
The hydro~yl number and the proportion of primary hydroxyl 25 groups are determined according to the method described in Analytical Chemistr;y 33 896 (1961).

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Extensive ir~vestigations have shown that one single polyol having properties corresponding to that of the polyol mixture does not produce a polyurethane from having the desiredproperties, nor does a poly~l mixture having properties other than those stated above.
An especially remarkable feature of the poiyurethane oams prepared according to the invention is that the extremely low hardness (i. e., super hypersoEtness~ can be combined with e2~cellent physical properties, such as elongation at break, tensile strength and compression set. Further, during the -Eoaming process the foam shows excellent stability. Thus, it is of decisive importance that the conditions according to the invention be met, since otherwise the stated beneEits of the invention will not be obtained.
The polyether polyols employed in the process of the invention are obtained by adding at least two different alkylene oxides, o-f --15 which one is ethylene oxide, to a poly~unctiDnal nucleus having at least three reactive hydrogens. This nucleus can be a polyol having at least three hydroxyl groups. Triols such as glycerol and trimethylolpropane are preferred, but trihydroxy alkanol amines such as triethanolamine are also useful. ~ The oxyethylene units of the polyether polyol mixture deriyed from ethylene oxide is from 50 to 70% by weight; the remaining oxyalkylene units derived from higher alkylene oxides can be from propylene oxide, butylene oxide, or migtures of these.
The addition o-E the all~ylene oxides is carried out by conventional methods. Ethylene oxide and higher alkylene oxi~es can be added either in admixture or separately, in one or more increments or , - 3 ~ ~

..

- . . .. . . . .

' " ' ' ' ~ . ' " ' ' , .. ' ' . `~ . ', ,' ., .. . ' . ' .', ' , . , ' . , batches. In order to obtain high so~tness it is essential that the two p~lyethe-r polyols be mutually insoluble, i. e. that they have different hydrophilicity.
The weight ratio of the polyether polyols should fall within the range from 1:lQ to 10:1.
One of the two polyols should be soluble in water, and should preferably have an HLB value of at least 15, and a turbidity p~int of at least 88C. Its a~erage molecular weight is from 3000 to 5000.
The other polyether polyol should be considerably more hydrophobic, alld should have an HLB ~alue not exceeding 5, and a turbidity 10 point of below 70C. The average molecular weight of this polyether polyol can be somewhat higher, and range from 3aoo to 70Q0.
The HLB values a:re calculated according to W. C. Griffin, Oficiai Digest, June 1956, 447, and the turbidity points are calculated according to Lowe et al~ Journal of Cellular Plastics, January 1965, 121.
Illustrative examples of suitable polyols according to the invention are the following:
EXAMPLE A
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O~ta. 92 parts by weight of glycerol there are first condensed 4, 000 parts by weight of propylene oxide, and thereupon 1300 parts by weight of ethylene oxide are condensed thereoll. The resulting polyether polyol adduct has a hydro~yl number of 36 and 75~c primary hydro~yl groups.
EXAM:?LE B
Onto 92 parts by weight of glycerol there are first condensed 470 parts by weight of propylene oxide, and thereupon 3440 parts by weight of a mi~ture comprising 18~C of propylene o~ide and 82C/C of ethylene o~{ide , ... . . . .. . .
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. .. .. , ~ , .

~os~oo are condensed thereon. The resulting polyetller polyol adduct has a hydroxyl number of 42, and 5~c/c primary hydroxyl groups.
EXAMPLE C
-Onto 134 parts by weight of trimethylolpropane there are first condensed 3000 parts by wei~ht of a mixture comprising 18'3ic of propylene oxide ancl 82% of ethylene oxide, and thereupon 300 parts by weight of propylene oxide and finally 350 parts by weight of ethylene oxide are condensed thereon. The resultmg polyol has a hydroxyl numbsr of 42, and ~3% primary hydro~yl groups.
EX~PLE D
r _ ' Onto~ 99 parts by wei~ght of glycerol there are first condensed 5000 parts by weight of propylene oxide and then 100 parts by weight of ethylene oxide. The resulting polyol has a hydroxyl number of about 34, and 7537c primary hydroxyl groups.
-- 15 The polyisocyanate to be used according to the present invention is at least bifunctional, but it can also be polyfunctional. Examples of suitable isocyanates are toluene diisocyanate, hexamethylene diisocyanate~
diphenylmethane diisocyanate, polyphenylpolymethylenepolyi$ocyanate, and mixtures thereof. The preferred isocyanate is toluene diisocyanate, which `
can be in its isomeric 2,4-form, or 2~6-form, or as mixtures of these isomeric forms. A suitable isomer mixture comprises about 80% of

2, 4-isomer and 20% of 2, 6-isomer, but other proportîons can also be used success~ully. The amount of isocyanate added should be adapted to the remaining components contained in the reaction mixture in such a way that the isocyanate index, i. e. the ratio between isocyanate groups an~ hydroxyl -. ~ ' .

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groups present in the mi~ture, is from about 0. 85 to about 1. 05, preferably from 0. 90 to û. 98 .
The reaction between isoc:yanate and polyether polyol is carried out in the presence of an amine catalyst, preferably a tertiary amine, such as triethylenediamine, dimethylaminoethanol; and tetramethvl-ethylenediamine. One can also use organometallic salt catalysts, such as tin-2-ethylhexoate, tin dibutyl dilaurate, lead naphthenate, and cobalt naphthenate; such salts are preferably used in small amounts, and in combinatlon with amine catalysts.
The cell formation and accordingly the density of the poly-urethane foam is controlled by adjusting, in a conventional way, theamount of water added and any other blowing agents, such as trichloroEluoromethane or methylene chloride. The addition af foam stabilizers, such as silicone oil, will ensure a good foam stability, and good physical strength properties.
In addition to the above-s$ated additives7 other addîtives can be added, if desired, using well-known techniques.
The following Examples in the opinion of the inventors represent preferred embodiments of thelr invention.
EX~IPLES 1 to 3 With the aid of a Eive-component laboratory foaming machine, a polyether polyol corresponding to 3xample A above was mixed with a polyether polyol corresponding to Example B above, waterJ silicone oil, triethylenediamine, dimethylaminoethanol and trichlorofluorome$hane in the parts by weight stated in Table I below, together with toluene diisocyanate (80% 2,4-isomer, 20~C 2,5-isomer) in an amount to bring the isocyanate ~, 1~516~
index to 0. 95. The mixture was poureA into a 50 x 50 x 30 cm mold and the resulting foam allowed to set for one day at room temperature. Upon con-ditioning for 24 hours in a cvnstant temperature room, physical tests were carried out. The following results were obtained:

T~13LE I
P rts by Weigh$
Formulation Example 1 Example 2 E~ample 3 Polyether polyol of Example A 25 25 25 Polyether polyol of Example B 75 75 75 Water - 3. 5 3. 5 3 5 Silicone oil 1.5 1.5 1.i5 Triethylenediamine (33%) 0.2 0.2 0.2 `
Dimethylaminoethanol 0. 8 0. 8 0. 8 Trichlorofluoromethane 15 7. 5 o -: :~

Toluene diisocyanate an amount to gîve - .
an isocyanate index of 0~ 95 `~

Physical properties (ASTM D 1564-62g~
Density, kg/m3 19.7 23.i5 27 . ~:
Tensile strength, kg/cm2 1.2 1. 3 1~ 7 . ~ ::
Elongation at break, ~c. 490 420 395 Teiar strength, kg/cm 0. 5 0.4 Q. 6 ~-90% corr~ression set, % 10 10 10 ;
Impact resilience, ~c . 50 50 50 -Hardness, 25(7c compression, kp/dm2 0.6 0~9 1 Hardness, 6D% connp ession, kp/dma7.2 I. 7 Z. 1 . . ' '' ' .

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From the results it is evi~ent that the foams are quite soft, i. e., they have an extremely low hardness. For comparison, the foam prepared according to the French patent specification No. 2,172, 860 at about the same density and about the same physical properties, has a 5 hardness twice that of Example 2.
EX~MPLES 4 TO 5 With the ald of a fi~e component laboratory foaming machine polyether polyol of Example D was mixed with polyether polyol of Example B
(which were mutually in~olu~le),water, silicone oil, triethylene diamine 10 and dimethylaminoethanol in the amounts stated in Table II below, together with toluene diisocyanate (80'3~c 2,4-isomer, 20% 2,6-isomer) in an amount to give an isocyanate inde~ of 0.~5. The mixture was poured into a 50 x 50 x 30 cm mold and the resulting foam was allowed to set for one day at room temperature. Upon conditioning for 24 hours in a constant - 15 temperature room, physical tests were carried out. The following result~ -were-obtained:

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TABLE II
Parts by Weight Formulation Example 4 Example 5 Polyether polyol of Example.D 20 30 Polyether polyol of Example B 80 ~ 70 Water 3. 5 3 5 Silicone oil 1.5 1.5 ~friethylenediamine (33%) 0.15 0.15f Dimethylaminoethanol 0. 55 0. 55 Toluene diisoc~anate an amount to give an isocyanate index of 0.95 Physical properties (ASTM D ff 5f64-629) ... .
Density, kg/m3 29 29 -; . .
Hardness~ 25% compression, kpf/dm2 . 1.3 . 1.ffJ -~
.,;, :: :
Ha~dness, 65% compression, kp/dm2 2. 5 ~. 0 The polyurethane fofams prepared showed, in af~dition to low hardness, exf~ellf3nt physical properties, such as a regular cell structure, a high elongation at breal~, and a high tensile strength. During i ~:
Ihe ioaming, no shrinkage is observed. ~

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Claims (5)

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. In the process for the preparation of soft highly hydrophilic polyurethane foam which comprises reacting a polyisocyanate with a polyether polyol in the presence of catalyst, blowing agent, and foam stabilizer, the improvement which comprises reacting with the polyisocyanate at least two mutually insoluble polyfunctional polyether polyols in amounts to provide a ratio of isocyanate groups to hydroxyl groups within the range from about 0.90 to about 0.98, the polyether polyol mixture having from about 50 to about 70% oxyethylene units, a hydroxyl number of from 35 to 45, and from 55 to 80% primary hydroxyl groups by weight of the total number of hydroxyl groups in the polyether polyol mixture.

2. A process according to claim 1, in which one of the polyether polyols is soluble in water.

3. A process according to claim 2, in which the water-soluble polyether polyol has an HLB value of at least 15 and a turbidity point of at least 88°C.

4. A process according to claim 19 in which one of the polyether polyols has an HLB value not exceeding 5, and a turbidity point of below 70 °C.

5. A process according to claim 1, in which the polyisocyanate is toluene diisocyanate.