CA1074950A - Silicate extended polyurethane foam - Google Patents

Abstract

(B) ABSTRACT OF THE DISCLOSURE
Polyurethane foam products having relatively noncombus-tible properties, low flame spread ratings and low smoke generating tendencies when burned can be produced by com-bining aqueous alkali metal silicate into the foam forming composition which customarily includes a polyol and a poly-isocyanate along with a suitable catalyst, surfactant and inert blowing agent. The aqueous alkali metal silicate content of the foam forming ingredients constitutes from about 10 to 60 percent by weight. Aqueous sodium silicate having a weight ratio of SiO2/Na2O of 2.40 to 3.25 is pre-ferred as the silicate ingredient.

Description

(D) BACKGROUND OF THE INVENTION
1. Field of the Invention: This invention relates to alkali metal silicate extended polyurethane foam systems.

2. Description of the Prior Art: Polyurethane foam technology is a highly developed art. Sales of polyurethane foam in 1970 exceeded 1 billion pounds in the United States.
In general polyurethane foam is produced by combining the following ingredients:

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1. A polyisocyanate 2. A polyol

3. A blowing agent, normally a halogenated hydL ocarbon

4. A suitable catalyst for the reaction of -OH and -N=C=O groups

5. A surfactant to control cell size and distribution Customarily a sufficient amount of polyisocyanate is pro-~10 vided to combine with the -OH groups of the polyol. The ` polyurethane foam has densities of about 2 pounds per cubic foot to about 40 pounds per cubic foot. The material has excellent thermal insulating properties. Polyurethane foam ~ is available in both rigid and flexible forms.
L5 In addition to the foregoing materials other additives may be employed such as:
1. Particulate fillers 2. Fibrous fillers 3. Pigments and dyes 4. Fire retardant additives which may be coreactive and which may constitute a part of the polyol ingredient 5. Water.
Polyurethane foams are employed as flotation elements for aquatic vessels, as thermal insulation for heat transfer \` , .

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barriers, as spacer members, as fillers and encapsulating materials for sealing cavities, as wall and ceiling cover-ings, and as packaging materials, and other uses.
United States Patent 3,607,794 (issued September 21, 1971) concerns the production of silicate foams by reacting an alkali metal silicate with a polyisocyanate in the absence of a preformed resin.
United States Patent 3,634,342 (issued January 11, 1972) is directed to the addition of small quantities of alkali metal silicate to polyurethane foam to permit the foam to be depotted when that is desired. The amount of alkali metal silicate for this purpose is from 0.5 to 5.0%.
The reference indicates that the action was too rapid to control when the amount of sodium silicate exceeded 5.0%.

(E) SUMMARY OF THE I~E~TION
The present invention relates to polyurethane foam systems for producing rigid polyurethane foams containing appreciable quantities of aqueous insoluble alkali metal silicates. According to the invention, the polyurethane foam system includes as its essential ingredients A. Polyisocyanate B. Polyol C. Blowing agent D. A catalyst for the reaction of -OH
-25 and -N-C=O groups E. A surfactant F. Aqueous alkali metal silicate Each of the ingredients A through E are found in conventional polyurethane foam systems. The aqueous alkali metal silicate provided in the present system serves to extend the polyurethane foam ingredients and achieves useful properties in the resulting silicate ex-tended polyurethane foam. The aqueous alkali metal silicate constitutes from about 10 to about 60 parts by weight of the total polyurethane foam system according to the present invention. The resulting silicate extended polyurethane foam has an alkali metal silicate content of about 7 to 50%
by weight. The polyisocyanate is provided in a sufficient quantity to supply -N=C=O equivalents for combining with all of the -OH groups in the polyol and some portion of the uncombined water which is provided with the aqueous alkali metal silicate solution. That is, an excess of -N-C=O
groups is supplied over that required to combine with all of the -OH groups of the polyol ingredient.
The foam can be applied by spraying or pouring. The , foam can be produced in a free-rise system or in a confined mold system. The resulting foams in general develop densities from about 2.0 to 40.0 pounds per cubic foot.
The resulting foams also develop a complex salt Na2CO3 NaHCO3 2H20 uniformly dispersed throughout the foam !

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mass as a result of the reaction of nascent carbon dioxide with sodium ions.

(F) BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a ternary diagram of the three component ~5 systems Na20, SiO2 and H20.

(G) DESCRIPTION OF THE PREFERRED EMBODIMENT(S) The present invention concerns the use of substantial quantities of aqueous alkali metal silicate as an ingre-dient in polyurethane foams produced by reaction of poly-.0 isocyanates and polyols.
The Silicate The preferred aqueous alkali metal silicate is aqueous sodium silicate which exists in the form of mixtures of SiO2 and Na20. The ratio of SiO2/Na20 for the present purposes :~5 is preferably from 2.40 to 3.25. Other suitable alkali metal silicates include potassium silicate and lithium silicate.
Referring to FIGURE 1, there is presented a ternary diagram for the system ~a20-SiO -H20 reproduced from Indus-trial and Engineering Chemistry, Volume 61, April 1969, page 32. Various areas of the drawing have been numbered to indicate commercial and noncommercial sodium silicate compositions.
Area 1 indicates highly alkaline mixtures including orthosilicate;

Area 2 indicates alkaline crystals, principally sodium metasilicate and its hydrates;
Area 3 defines the compositions from which com-mercial glasses are produced;
Area 4 indicates hydrated amorphous (spray dried) powders;
Area 5 is the commercial aqueous sodium silicate solutions;
Area 6 indicates partially crystallized mixtures;
Area 7 indicates uneconomical hydrated glasses;
Area 8 indicates semi-solid masses;
: Area 9 indicates very viscous liquids;
Area lO indicates dilute liquids;
Area ll indicates unstable liquids and gels.
In general, the aqueous sodium silicates which are useful ~; in the practice at the present invention are those encom-passed within Area 5 of the ternary diagram of FIGURE l.
Aqueous sodium silicate compositions within Area 9 of the ternary diagram of FIGURE l can be employed if their viscosity is reduced by mixing with some of the other foam forming ingredients or by dilution with water or with miscible glycols.
The Polyol .
The polyol employed in the present formulation may be a hydroxy-ester, a glycol, a polyhydric alcohol, a hydroxy-\

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terminated polyester, a polyether or a polyester-polyether.
Useful polyesters include the condensation reaction prod-ucts of polycarboxylic acids with polyols. Useful poly-ethers incl~de polyalkylene oxide adducts ~uch as poly-ethylene oxide adducts or polypropylene oxide adducts of base materials having at least 2 active hydrogen atoms as determined by the Zerewitinoff method. Adducts of glycols, triols, tetrols, higher polyols, amines, amides are useful and are well known in the art as typical polyurethane .0 polyols. Other polyester-polyethers can be prepared by etherification of polyesters or by esterification of poly-ethers. The polyol is maintained essentially anhydrous to minimi7e unwanted reaction of the -N=C=O groups of the polyisocyanate during foam-formation.
L5 Hydroxyl amines and hydroxyl polyamines can be employed as a substitute for a portion (up to about 10 percent by ` weight) of the polyol ingredient as reactive modifiers.
The use of hydroxyl polyamines is especially helpful to adjust the viscosity of the polyol component where some viscosity control is desired.
The PolYisocyanate The organic polyisocyanate preferably is a polymeric polyisocyanate or a prepolymer or a quasi-prepolymer. Pre-ferred polyisocyanates are polymethylene-polyphenylene-polyisocyanate, \

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aliphatic diisocyanates and in general any polyisocyanate having molecular weight greater than 250. Other preferred polyisocyanates are the prepolymers which are fabricated by combining any suitable polyisocyanate with polyol. One example is the adduct formed by TDI (toluene diisocyanate) with glycol or other polyols. Quasi-prepolymers also are useful in the poly-isocyanate, for example, the quasi-prepolymer formed by combining a stoichiometric excess of polymethylene-poly-phenylene-polyisocyanate with glycol. The polyisocyanate is maintained in essentially anhydrous condition since the -N=C=O groups react with water.
Reinforcinq Modifiers As a refinement of the present invention, improved strength properties are achieved when the foam forming mixture also includes reinforcing resins such as melamine-formaldehyde, methylolated melamine formaldehyde, urea formaldehyde and phenolic resins. The melamine and urea resins are useful when present in amounts from 0.1 to 5 weight percent of the formulation Phenolic resins are useful in quantities of about 0.1 to 2 weight percent of the formulation. The modifying resins generally increase the physical properties of the resulting foam, e.g., tensile and compressive strength. Formaldehyde alone also is a useful additive in quantities from 0.1 to 5 weight percent.

, , Catalyst .

Several catalysts are contemplated in the present invention The principal catalyst is the urethane catalyst which is employed to accelerate the reaction between -OH
groups and -N=C=O groups. Examples are tin catalysts (stannous octoate; dibutyl tin dilaurate) and the amine catalysts (triethylene diamine, N,N,N',N'-tetra methyl butane diamine). The catalysts normally are provided in sufficient quantities to complete the urethane forming reaction ~enerally polyurethane foam systems employ about 1% by weight of catalyst based on the total foam weight.
In the present invention, the catalyst may be provided in lesser amounts. A preferred catalyst content is about 0.2 to 0.3 percent by weight of the total foam, although the catalyst may range from 0.1 to 3.0 percent of the weight.
A secondary catalyst may be employed to bring about the independent curing of reinforcing resins such as melamines or urea-melamines. A typical secondary catalyst is para-toluene sulfonic acid which is supplied in accor-dance with the content of reinforcing resins, e.g., about 0.5 to 3 percent of the weight of the reinforcing resin.
Surfactants The surfactant should be hydrolytically stable materials, A preferably a silicone compound such as L-5310, L-530~ DC-194, DC-193 which are commercially available from Union Carbide \

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Corporation and Dow Corning Company respectively. The amount of surfactant preferably ranges from about 0.5 to 0.75 percent by weight of the total foam.
Blowin~ Aqents Preferably the halogenated hydrocarbon blowing agents are employed and are included in the polyol component or in the polyisocyanate component or divided between the two components. Freon llB (fluorotrichloromethane) is a pre-ferred blowing agent. Carbon dioxide and other highly 0 volatile, miscible materials may be employed as blowing agentS .
ViscositY Considerations The viscosity of the resulting mixture of polyol, poly-isocyanate, catalyst, surfactant, blowing agent and aqueous ~L5 alkali metal silicate should be suitable to accomplish thorough dispersion of the ingredients in a mixing device.
The dispersion should develop adequate flowing properties when the foaming mixture is deposited in a mold. The flowing properties are somewhat related to the gel time of the composition which in turn is related to the nature, amount and identity of the foaming catalyst. The viscosity should be sufficiently high to retard any collapsing tendency of the rising foam. Preferably the viscosity should be within the range of 1,000 to 2,000 centipoises.
The resulting alkali metal silicate extended polyurethane ~J~

-107~950 foam exhibits good adhesion to metal surfaces. The silicate extended polyurethane foam has fire retardant properties which are superior to the fire retardant properties which would be achieved from the identical polyol and polyiso-cyanate alone (assuming that proper stoichiometric adjust-ments are made for the comparison). The improved results are evidenced by flame spread tests and burnthrough tests.
Silicate extended polyurethane foam develops a dimensionally stable char when exposed to direct flame impingement. The char resists further burn-out of the subjacent silicate extended polyurethane foam. The present silicate extended polyurethane foam has good humid aging characteristics when exposed to 100% humidity at elevated temperatures, The thermal insulating property of the present silicate ex-~15 tended polyurethane foam is greater than the thermal insulating property of many commercially employed thermal insulating substances, although the thermal insulating property is not as good as that of conventional polyurethane foam which does not contain the aqueous alkali metal silicate.
~20 The present silicate extended polyurethane foam has a lower materials cost when compared with conventional organic polyurethane foam of the same density, The present silicate extended polyurethane foam can be adapted to employ existing polyurethane foam technology and existing foam mixing and dispensing equipment including spray nozzles and the like, 1074g50 When the silicate extended polyurethane foam is compared with the polyurethane foam of the same density, the tensile strength and compressive strength of the silicate extended polyurethane foam is somewhat less but nonetheless commercially useful and significant.
Example 1 A silicate extended polyurethane foam is prepared by combining the following ingredients:
Component A
0 7,491 grams of hydroxyl terminated polyester mixture hereinafter more particularly described;
24.75 grams of surfactant, specifically L-5310 which is a silicone surfactant available .S from Union Carbide Corporation;
8.25 grams of a catalyst, specifically triethylene diamine commercially available under the trade name DABCO from Houdry Processing Company;
1.65 grams of a catalyst which is N,N,N',N'-tetra '0 methyl butane diamine;
173.75 grams fluorotrichloromethane The hydroxyl terminated polyol mixture of Component A is a polyesterification product of 32.79 grams trimethylol propane;
~5 3,73 grams 1,6-hexane diol;

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1074~50 13.68 grams adipic acid;
25.55 grams tetrabromophthalic anhydride.
These ingredients are cooked to an acid number less than 1. 71.6 parts by weight of this described polyol are combined with 1.40 parts by weight of hydrolytically stable silicone fluid, 0.75 parts by weight of triethylene diamine solution, 26.1 grams of fluorotrichloromethane and 0.15 parts by weight N,N,N',N' tetra methyl butane diamine.
The described mixture totals 100 parts by weight and is O the hydroxyl terminated polyester ingredient of Component A.
Component B
7,491 grams of a polyisocyanate prepolymer, which is more fully described hereinafter;
~ 749.1 grams of FREON llB~ i.e., fluorotrichloro-methane;
2.80 grams of a surfactant, specifically L-530 which is a silicone surfactant available from Union Carbide Corporation;
184.8 grams of a flame retardant additive, 'O specifically Phosgard C-22R which is a polymeric halogen containing phosphate available from Monsanto chemical Corporation.
Phosgard C-22R~has the following structural formula:

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C1-CH2CH20POCHPOCHP-(OCH2cH2cl)2 C lCH2CH2 OCH2CH2C 1 ~.

fr~ J~ 13--, The polyisocyanate prepolymer described as an ingredient of Component B is formulated by cor~ining 79.88 parts by weight of crude polymethylene polyphenylene diisocyanate;
2.50 parts by weight of methyl glucoside based polyether;
1.12 parts by weight silicone fluid, L-5310 available from Union Carbide Corporation;
16.50 parts by weight Phosgard C-22R.
~:10 The ingredients are mixed and heated to 170-180F and held - at that temperature for about one hour until substantially all of the hydroxyl groups are combined with isocyanate groups. The resulting prepolymer material has a -N=C=O
value of about 23-25.
ComPonent C
Aqueous sodium silicate having a weight ratio of SiO2/Na2O of 2.50;
a Baume density of 42;
a viscosity of 60 centipoises measured at 68F;
. 20 a percentage of Na2O of 10.60 and a percentage of Sio2 of 26.5.
The aqueous sodium silicate of this example is com- ~:
mercially available from Philadelphia Quartz Company under the grade designation STAR sodium silicate. The expression STAR sodium silicate is sometimes employed hereinafter to Y,~ .

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f~ Jc~n~ -14-: - ' ' : ' -~ "' '' "" '"' '' .'. ~ ' ' 1074~50 identify this aqueous sodium silicate which has been fully described in this Example 1.
All of the three components A, s and C are combined in the approximate ratio of 1 part A, 1.7 parts B, and 2.2 parts C~ More specifically, 20.25 grams of A, 34.7 grams of B, and 45.05 grams of C are mixed in a paper cup with a rotary blade mixer for ten seconds until cream is observed. The mixed ingredients are allowed to rise in the paper cup to produce a uniformly cellular foam having .0 a density of 3 pounds per cubic foot The foam is white in color and has a uniform fine cell structure.
; The a~ueous sodium silicate constitutes 56.5 welght - percent of the total formulation.
Polyurethane foam as described in Example 1 was deposited !5 between two flat steel sheets 1-1/2" apart and measuring 36" x 45". The sheets were clamped in fixed, parallel, opposed relation to each other. The creaming mixture was deposited and allowed to rise in contact with the two steel plates. The alkali metal silicate extended polyurethane foam ~0 exhibited good adhesion to the steel plates. The foam also exhibited good humid aging characteristics when exposed to ASTM test D-2247.
Example 2 Component A was prepared by combining 26.4 pounds of the hydroxyl-terminated polyol `~

described in ~xample l;
3.5 pounds formaldehyde;
8.8 pounds Cymel 303 (a melamine resin of A,.~erican Cyanamid Corporation);
~5 0.2 pounds catalyst 1010, (a melamine con-densation catalyst, specifically p-toluene sulfonic acid); and 0.2 pounds of R-8020 which is a reaction catalyst for urethane, specifically, a mixture of 0 triethylene diamine and dimethyl ethanolamine, available from Houdry Processing Company.
Component B was prepared by combining 31.5 pounds of the polyisocyanate prepolymer of Example l;
LS 2.9 pounds of L-530 (silicone surfactant);

6.3 pounds Phosgard C-22R (fire retardant additive); and 9.5 pounds fluorotrichloromethane.
Component C was 100 grams of STAR aqueous sodium silicate, available from Philadelphia Quartz Company, hereinabove described.
A foam was prepared by combining 100 grams of Component C with 20.8 grams of Component A and 79.2 grams of Component B. The three components were mixed with a rotary mixer for ten seconds at number 4 speed in a cup. The cream time was ~ ~r~ ~e ~ -16-107~95~) 30 seconds, the tack time was 120 seconds, the rise time was 210 seconds. The material was poured onto a steel plate at 108F. The material produced a stable foam.
After 24 hours a sample of the foam was cut. The cut sample evidenced no shrinkage. The foam had a density of 4.31 pounds per cubic foot. The closed cell content of the foam was 70.8%.
The aqueous sodium silicate constituted 50 weight percent of the total formulation.
Example 3 23.2 grams of Component A (as in Example 2) and 88.4 grams of Component B (as in Example 2) were combined with 88.4 grams of STAR aqueous sodium silicate. The three com-ponents were mixed with a rotary mixer, number 4 speed, for ten seconds and poured onto a steel plate at 104F. The composition had a cream time of 30 seconds, a tack time of 120 seconds and a rise time of 210 seconds. A sample of the resulting foam exhibited no shrinkage after 24 hours.
The foam had an average density of 3.13 pounds per cubic foot and an average closed cell concentration of 77.5%.
The aqueous sodium silicate constitutes 44.2 weight percent of the total formulation.
Example 4 32.8 grams of Component A (as in Example 2) and 127.2 grams of Component B (as in Example 2) were mixed with 40.0 ,, \

, grams of STAR aqueous sodium silicate. The mixture was mixed with a rotary mixer at number 4 speed for ten seconds.
The mixture was applied to a steel substrate at 106F. The mixture exhibited a cream time of 5 seconds, a tack time of 90 seconds and a rise time of 150 seconds. The foam sample exhibited no shrinkage when cut after 24 hours. The average density of the material was 1.56 pounds per cubic foot.
The aqueous sodium silicate constitutes 20 weight percent of the total formulation.
ExamPle 5 A sample of the present foam was prepared employing approximately half the normal amount of silicone surfactant.
To prepare this foam Component B was prepared by combining 83.1 grams of the polyisocyanate prepolymer of Example l;
16.5 grams of Phosgard C-22R flame retardant;
0.9 grams of L-530 silicone surfactant; and 25.2 grams of Freon llB.
The foam composition was prepared by combining 88.4 grams of Component C (STAR aqueous sodium silicate); 23.2 grams of Component A (as in Example 2); and 85.8 grams of Com-ponent B as herein described. The ingredients were mixed with a rotary mixer for ten seconds at number 4 speed. The mixed ingredients were applied to a substrate at 108F. A
cream time of 25 seconds, a tack time of 120 seconds and a ~07f~9S0 rise time of 200 seconds was observed. The foam had a good rise and appeared dry. The foam exhibited no shrinkage after 24 hours. The foam had an average density of 3.11 pounds per c~bic foot, The foam had an average closed cell content of 52.2%. The foam had a tensile strength of 20.1 psi. The aqueo~s sodium silicate content of the formulation was about 45 percent by weight.
Example 6 A number of different commercially available aqueous sodium silicate materials were evaluated including the STAR
aqueous sodium silicate described in Example 1.
The specific aqueous sodium silicate of this Example 6 is a material known as Starso which has a density of 1.80;
a Baume gravity of 44.6; SiO2/Na20 weight ratio is 1.80;
weight percent ~a2O is 13.40; weight percent SiO2 is 24.1.
In this Example, 88.4 grams of the Starso aqueous sodium silicate (Component C) was combined with 23.2 grams of Component A (as in Example 2) and 88.4 grams of Component B (as in Example 2). The components were mixed with a rotary mixer for ten seconds at number 4 speed. The material foamed in the mixing cup---exhibiting a rapid cream time. A second batch was prepared and mixed for five seconds with a rotary mixer at number 4 speed. In this case the cream time was approximately zero seconds, the tack time was 90 seconds and the rise time 120 seconds when the material was poured 1074950 , onto the substrate at 1080F. The foam had a density of 2.52 pounds per cubic foot and a closed cell content of 14.0%. The tensile strength was 4.5 psi. The foam was generally ra'her weak.
Example 7 A foam was prepared without using foaming catalysts.
The following ingredients were mixed together to produce Component A:
78.30 grams of the hydroxyl-terminated polyol LO ingredient of Example l;
10.40 grams formaldehyde;
26.10 grams Cymel 303~(hexamethylol melamine resin); and 0.60 grams of catalyst lOlO~tp-toluene L5 sulfonic acid).
This Component A for this formulation contains no urethane catalyst.
23.0 grams of Component A as just described was com-bined with 88.4 grams of Component C (STAR aqueous sodium silicate) and 88.4 grams of Component B (as in Example 2).
The three components were mixed with a rotary mixer for ten seconds at number 4 speed and applied to a substrate at 108F. The cream time was 25 seconds, the tack time was 180 seconds and the rise time 180-240 seconds. The resulting foam was dry and exhibited a good rise. The foam had a very \

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107~951~) slight shrinkage after 24 hours. The density of the foam was 4.06 pounds per cubic foot. The closed cell concentra-tion was 26.5%. The tensile strength was 21.7 psi. An interesting feature in this example is that the present foam can be prepared without a urethane catalyst although the cream time, rise time and tack time are extended.
The aqueous sodium silicate constituted 44 weight percent of the total formulation, ExamPle 8 L0 A foam was prepared incorporating m~thylolated urea, specifically Beetle 65 (methylolated urea) which is produced by American Cyanamid Corporation. Component A was prepared by combining 78.3 grams of the hydroxyl-terminated polyol of L5 Example l;
10.4 grams of formaldehyde;
26.7 grams of Beetle 65~(urea);
0.6 grams catalyst 1010 (p-toluene sulfonic acid); and 0.6 grams of R-8020 catalyst.
23.3 grams of the special Component A as just described was combined with 88.4 grams of Component C (STAR aqueous sodium silicate) and 88.4 grams of Component B as in Example 2.
The mixture was mixed with a rotary mixer at number 4 speed for ten seconds and poured onto a substrate at 108F. The ~r~

material had a cream time of 20 seconds, a tack time of 180 seconds and a rise time of 255 seconds. The material formed a foam which exhibited a slight shrinkage after 24 hours. The resulting foam had an average density of 4.26 pounds per cubic foot. The closed cell content was 67.5%.
The tensile strength was 14.4 psi.
The aqueo~s sodium silicate constituted 44 weight percent of the total formulation.
Example 9 0 This example, similar to Example 1, does not include melamine resin or formaldehyde.
Component A was prepared by combining 15.6 grams of the hydroxyl-terminated polyol of Example l; and 0.12 grams of catalyst R-8020.
This Component A was comhined with 88.4 grams of Component C (STAR aqueous sodium silicate). Mixing of the two Com-ponents A and C was difficult but adequate mixture was achieved. Thereafter 88.4 grams of Component B (as in ~O Example 2) was combined and the ingredients were mixed with a rotary mixer for ten seconds at number 4 speed and poured onto a substrate at 108F, The cream time was 25 seconds, the tack time was 120 seconds and the rise time was 180 seconds. The foam exhibited a good, high rise and a firm ~5 set up. There was a slight shrinkage after 24 ho~rs. The * ~ -22-~ --~

closed cell content of the foam was 47.2%. The density was 2.82 pounds per cubic foot, The tensile strength was 18.1 psi. In the absence of formaldehyde and melamine the resulting foam generally has a lower closed cell content and reduced tensile strength.
The aqueous sodium silicate constituted 46 weight percent of the total formulation, Example 10 The present foam can be obtained in the absence of 0 formaldehyde using a melamine resin alone.
Component A was prepared by combining 15.6 parts of the hydroxyl-terminated polyol of Example l;
~ 5.22 parts by weight of Cymel 303~(melamine resin);
'5 0.12 parts of catalyst lOlO~(p-toluene sulfonic acid); and 0.12 parts of catalyst R-8020.
This Component A was combined with 88.4 parts by weight of Component C (STAR aqueous sodium silicate). There was some emulsification difficulty during the mixing but ultimately adequate mixture was achieved. Thereafter 88.4 parts of Component B (as in Example 2) was mixed with Components ~
and C for ten seconds at number 4 speed with a rotary mixer.
The resulting mixture was applied to a substrate at 108F.
The cream time was 30 seconds, the tack time was 120 seconds ~ r~Je~fk -23-107~95V

and the rise time was 240 seconds. The foam exhibited a slight shrinkage after 24 hours. The density of the foam was 3.32 pounds per cubic foot. The closed cell content was 57.0%. The foam had a tensile strength of 17.5 psi.
The aqueous sodium silicate constituted 46 weight percent of the total formulation.
Example 11 This example ill~strates the use of a polyether polyol, ~ specifically Jefferson HD-780~ as the polyol ingredient.
.0 Jefferson HD-780 is a sucrose-based polyol having an OH-equivalent of 338, an acid number of 0.2, pH 5.2 and a viscosity at room temperature of 7600 centipoises. Component A for this example was prepared by combining 264 grams Jefferson HD-780 !S 35 grams formaldehyde 80 grams Cymel 303 (melamine resin) 2 grams catalyst 1010 (p-toluene sulfonic acid) 2 grams catalyst R-8020 23.0 grams of Component A as just described was combined with 88.4 grams of Component C (STAR aqueous sodium silicate) and 88.4 grams of Component B (as an Example 2). The mixture was mixed with a rotary mixer for ten seconds at number 4 speed and applied to a substrate at 108F. The cream time was 30 seconds, the tack time was 240 seconds and the rise time was 240-300 seconds. A foam was prepared which exhibited -~ 7 r~ 24-very slow setting. The foam had a streaky composition and a nonhomogeneous cell structure. The foam had a density of 2.70 pounds per cubic foot. The closed cell structure was 48.1%. The tensile strength was 6.1 psi.
The aqueous sodium silicate constituted 44 weight percent of the total formulation.
Example 12 This example shows the use of a polyester polyol.
Component A was prepared by combining the following ingre-L0 dients:
78.3 grams Mobay Multron R-4 10.4 grams formaldehyde 26.1 grams Cymel 303 (melamine resin) 0.6 grams catalyst 1010 (p-toluene sulfonic acid) L5 0.6 grams catalyst R-8020 The Multron R-4~is a saturated linear polyester having an equivalent weight of 200, an acid number of 4 and a hydroxyl value of 270 to 290. The material is commercially available as a polyol ingredient for use in urethane foams and elas-tomers. It is available from Mobay Chemical Company.
In order to prepare a foam, 23~3 grams of Component A
as just described was combined with 88.4 grams of Component C (STAR aqueous sodium silicate) and 88.4 grams of Component B (as in Example 2). The three components were mixed with a rotary mixer for ten seconds at number 4 speed and poured \~

~ r~ ~e ~ ~ 25-onto a substrate at 108F. The material had a cream time of 35-40 seconds, a tack time of 210 seconds, a rise time of 300 seconds. The foam had a slow rise and remained soft. Aqueous sodium silicate could be squeezed from the foam. The foam was streaky and exhibited a non-homogeneous cell structure. The foam had a density of 3.38 pounds per cubic foot. Closed cell content was 43.9 percent.
Example 13 Another commercially available aqueous sodium silicate ,. ~f is known as N-38, available from Philadelphia Quartz Company.
N-38 aqueous sodium silicate has a SiO2/Na2O ratio of 3.22 and a Baume density of 38. The following ingredients were combined and mixed with a rotary mixer for ten seconds at number 4 speed:
88.4 grams of N-38~sodium silicate (Component C) 23.2 grams of Component A as described in Example 2 88.4 grams of ~omponent B as described in Example 2 The material was applied to a substrate at 1080F and exhib-ited a cream time of 45 seconds, a tack time of 180-240 seconds and a rise time of 180-240 seconds. The foam ex- ,-hibited nonhomogeneous structure and severe streakiness.
The density was 3.01 pounds per cubic foot. The closed cell content was 54.9 percent and the tensile strength was 11.4 psi.

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Example 14 Another commercially available aqueous sodium silicate is Diamond Shamrock chemical Corporation grade 50 which has the followi~g composition Na2O content of 14.7 weight percent; SiO2 content of 29.4 weight percent; and a SiO2/Na2O
ratio of 2.00. The density is 50 Baume and the viscosity is 122 Stormer seconds. A foam was prepared from 32 grams of Component A (as in Example 1); 120 grams of Component B
(as in Example 2); and 120 grams of Component C (Diamond L0 Shamrock grade 50 aqueous sodium silicate~. The eomponents were mixed for 5 seconds at 1900 RPM. A eream time less than 5 seconds was exhibited. The material foamed in the eup rapidly. The foam had a density of 2.58 pounds per cubic foot and an average tensile strength of 3.3 psi and a closed L5 cell content of 42.1 percent.
Example 15 A foam was prepared with Diamond Shamrock Chemical Corporation aqueous sodium silicate grade 52 which has a Na2O content of 13.9 weight percent; a SiO2 eontent of 33.4 weight percent; and a SiO2/~a2O ratio of 2.40. The density is 52 Baume and the viscosity is 640 Stormer seeonds. A
sodium silieate extended polyurethane foam was prepared by eombining 120 grams of Component C (grade 52 aqueous sodium silieate) with 32 grams of Component A (as in Example 2) and 120 grams of Component B (as in Example 2). The mixture was mixed with a rotary mixer for 5 seconds at 1900 RPM
exhibiting a cream time of 15 seconds, a tack time of 60 seconds, and a rise time of 120 seconds. The foam had a density of 2.63 pounds per cubic foot, a tensile strength of 2.6 psi and a closed cell content of 32u7 percent.
The aqueous sodium silicate constituted 44 weight percent of the total formulation.
Example 16 This is a further example of aqueous sodium silicate L0 extended polyurethane foam without melamine resin additives.
Component A was prepared by combining:
379 grams of the hydroxyl-terminated polyester of Example l;
50 grams of formaldehyde; and L5 ~ 2.0 grams of R-8020 catalyst.
Component B was prepared by combining:
329.5 grams of Papi-18~(a polyisocyanate of polymethylene polyphenylene);
66 grams of Phosgard C-22R flame retardant;
`20 26.5 grams of ~-5410 silicone surfactant; and 150 grams Freon 11B.
A polyurethane foam forming formulation was prepared by combining 32 grams of Component A as described with 120 grams of Component C (STAR aqueous sodium silicate) and 120 grams of Component s as described.

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The mixture was mixed with a rotary mixer for 10 seconds and exhibited a cream time of 10 seconds, a tack time of 120 seconds and a rise time of 120 seconds. The composition was slow in setting but firmed in about 15 minutes. The foam was generally weak and friable. The closed cell content was 1%, The density was 2.36 pounds per cubic foot, Example 17 Component A was prepared by combining L0 67.5 parts by weight of the hydroxyl-terminated polyester of Example l;
9 parts by weight formaldehyde (formalin);
22.5 parts by weight cymel 303*me`Lamine resin;
0.5 parts by weight catalyst 1010 - para toluene L5 sulfonic acid; and 0.5 parts by weight catalyst R-8020 triethylene diamine.
Component B was prepared by combining 62.8 parts by weight of polyisocyanate prepolymer of Example l;
5.95 parts by weight of L-530 silicone surfactant;
12.54 parts by weight Phosgard C-22R flame retardant plasticizer; and 18.90 parts by weight fluorotrichloromethane.
Component C was STAR aqueous sodium silicate.

~ e ~ ~f~ -29-~074950 This formulation, hereinafter referred to as "Example 17 formulation" is combined and mixed in the following proportions 11.6 parts by weight Component A; 44.2 parts by weight Component B; 44.2 parts by weight Component C.
The mixture exhibited a cream time of 30-40 seconds, a tack time of 3 1/2-4 minutes and a rise time of 3 1/2-4 minutes.
The "Example 17 formulation" was extensively tested with the following results.
A series of experimental panels was prepared with the L0 "Example 17 formulationl' sandwiched between two metal sheets. The "Example 17 formulation" foam had a density of 3.41 pounds per cubic foot and a closed cell content of 86% when the foam is formed under confinement between the metal sheets. The free rise properties of the "Example 17 formulationl' foam showed a density of 2.42 pounds per ` cubic foot and a closed cell content of 77%.
Samples of the resulting "Example 17 formulation" foam from the metal sided panels had a tensile strength of 23.3 psi .
Each panel had a thickness of 1 1/2" and an area of 35" by 45". The panels were completely filled within about 25 seconds.
Corner Burninq Tests A modified corner burning test has been developed in which two panels, each 4 feet long, are fastened together ~', \, .

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to form a corner. Wood sticks, paper and gasoline are collected in the corner and ignited. The present "Example 17 for,mulation" foam did not exhibit any initial burst of flame. During the fire there was some light, white smoke.
There was very little climbing of the flame over the panel surface. The panels had exposed foam on the fire side and metal skin on the surface away from the fire.
Burnthrouqh Tests The U.S. Bureau of Mines has established a burnthrough test which employs a propane gas torch having its flame impinging at right angles to the surface of a slab of polyurethane foam having an area approximately 6" by 6" and thickness exactly 1". The objective of the test is to de-termine the amount of time required for the flame to burst through the back side of the polyurethane slab from the time the torch is ignited. Conventional polyurethane foam exhibits burnthrough times of 10 seconds or less. A sample of the present "Example 17 formulation" foam required 180 seconds for burnthrough.
Thermal ConductivitY
A sample of "Example 17 formulation" foam was tested for thermal conductivity properties. The sample was 1.04"
thick, had a density 3.44 pounds per cubic foot. Thermal conductivity factor K was 0.169 BTU per hour per square foot per degree F. Temperature differential during the ~.

test was 97.4F on the hot side and 52.5F on the cold side.
Humidity Aqinq The "Example 17 formulation" foam was subjected to humidity aging tests. Samples were maintained at 100%
humidity and 120F for extended periods of time The properties of the samples at various times during the tests were measured. In each instance the sample was allowed to drain free of water before measurement. The L0 results are set forth in the following table:

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Example 18 A foam system herein identified as the "Example 18 formulation" was prepared and tested.
Component A was prepared by combining:
380 parts of the hydroxyl-terminated polyester of Example 1, parts 37% formaldehyde (formalin);
32.5 parts Cymel 303~(melamine resin);
1.5 parts catalyst 1010 (p-toluene sulfonic ~lO acid);
parts catalyst R-8020 parts DMP-30 (a phenol type amine catalyst manufactured by Rohm and Haas);

7 parts L-530 silicone surfactant; and 90 parts fluorotrichloromethane.
581 parts Component B was prepared by combining:
330 parts Papi-27/Neopentyl glycol prepolymer (formation here nafter described);
80 parts Phosgard C-22 flame retardant;
7 parts L-530 silicone surfactant; and parts fluorotrichloromethane 507 parts Component C was prepared by combining 300 parts of foundry grade aqueous sodium silicate with 20 parts of water 7rr~c~n~

having a total of 320 parts, Specifically the aqueous sodium silicate was Diamond Shamrock Chemical Corporation grade 49FG having a SiO2/Na2O ratio of 2.58 and a Baume gravity of ~9, The mixing ratio to produce a foam is 40 parts ~y weight of Component A, 112 parts by weight of Component B and 150 parts by weight of Component C.
The prepolymer in Component B is prepared by mixing ~ 19 parts by weight of Papi-27~a polyisocyanate of poly-L0 methylene polyphenylene having a functionality of about 3.0) with one part by weight of NPG (neopentyl glycol).
The addition is carried out at about 230F. The neopentyl glycol is added in approximately eight aliquot portions, one every five minutes with agitation. The reaction L5 develops a strong exotherm. A final viscosity of the pre-polymer in Component B ranges from about 185,000 to 200,000 cps .
The resulting foam has a cream time of 15 seconds, a tack time of 60 seconds and a rise time of 70 seconds. The foam has 76% closed cell content, 3.5 pounds per cubic foot density, This material was subjected to a burnthrough test as described in Example 17. The burnthrough time was 13 minutes.

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Example 19 Another useful foam system was identified as "~xample 19 formulation".
Compon~nt A was prepared by combining:
379 grams of the hydroxyl-terminated polyester of Example l;
50 grams formaldehyde (formalin);
31.5 grams Cymel 303 (melamine resin);
0.8 grams catalyst lOlO~(p-toluene sulfonic acid3;
.0 2.9 grams catalyst R-8020;
14.5 grams catalyst DMP-30 ta phenol-type amine catalyst manufactured by Rohm ~ Haas Corporation);
107.7 grams L-5410 silicone surfactant; and 438.0 grams fluorotrichloromethane.
L5 Component A had a Brookfield viscosity at 70F of 960 centi-poises.
Component B was prepared by combining:
660.0 grams Papi-28 (polyisocyanate of polymethylene polyphenylene);
122.0 grams Phosgard C-22R flame retardant;
4.5 grams L-5310 silicone surfactant.
Component B had a Brookfield viscosity of 600 cps at 70F.
A polyurethane foam was prepared by combining 57.2 grams of Component A as described with 94.8 grams of Com-ponent B as described and 120.0 grams of Component C which was aqueous sodium silicate 49FG (see Example 18). The total "Example 19 formulation" contained 272.0 grams.
The mixture was mixed for ten seconds. A cream time of 10 seconds, a tack time of 70 seconds and a rise time of 120 seconds was observed. The resulting foam had approxi-mately 3% closed cell content.
This "Example 19 formulation" foam was subjected to a burnthrough test by preparing a sample 6" square by 1"
thick as described in Example 23. The burnthrough test L0 required more than 30 minutes.
Composition of the Resultinq Foam X-ray analyses of products of Examples 1 and 18 indi-cated some crystalline silicates in the resulting foam.
The foams also indicate an x-ray pattern which is charac-teristic of a complex sodium carbonate and sodium bicar-bonate salt at a level of about 5 to 15% by weight. The complex salt has the following empirical structure~

It has been speculated that these complex salts are formed by reaction of the carbon dioxide which is evolved in the reaction of isocyanates with water. The carbon dioxide combines readily with the sodium silicate Na2SiO
to form the sodium carbonates and bicarbonates. The sodium carbonate and bicarbonate complex readily absorbs water from the system as water of crystallization.

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, -~07495() This mechanism in part accounts for the fact that the foam products appear to be essentially free of uncom-bined water despite the fact that the starting aqueous sodium silicate ingredient constitutes from about 7 to 50 percent of the weight of the resulting foam.
The rate at which the carbon dioxide is evolved from the foam seems to be important with respect to the character of the silica gel which results. Extremely rapid evolution of carbon dioxide gels SiO2 in a glass type structure. A
~0 slow release of carbon dioxide tends to precipitate SiO2 which forms spherical colloidal silica particles of approxi-mately 15 millimicrons diameter. These silica particles thereafter form a gel. The analyses indicated that the silica gel in the present polyurethane foams is a hybrid .5 mixture of the two types of gel just described.
Example 20 - A series of foam products was prepared utilizing the saturated polyester resin of Example 1 as the polyol ingre-dient and a polymeric MDI prepolymer as the isocyanate in-!0 gredient. Component A contained 11.51 parts by weight of the polyester, 3.00 parts by weight of fluorotrichloro-methane, 1.0 parts by weight silicone fluid as a surfactant and 0.25 parts by weight of a blend of txiethylene diamine and dimethyl ethynol amine as a catalyst.
~5 The polyisocyanate prepolymer was formed by combining .
' polymeric MDI, a sorbitol polyether having the hydroxyl value of 490-500, a silicone fluid as a surfactant and Q Phosgard C-22 ~ The prepolymer had an NC0 content of 23 to 24 percent by weight.
Component B was prepared by combining 33.52 parts by weight of the described polyisocyanate prepolymer; 1.22 parts by weight of silicone fluid as a surfactant; and 5.38 parts by weight of fluorotrichloromethane as a blowing agent, Component C in this series of foam preparations was commercially available aqueous sodium silicate, including:
SiO2~Na20 Ratio Baume Density (a)"5TAR" 2.50 37.1 (b) -- 1.60 51.1 15 (c)N-38 ~ 3.22 37.6 (d) -- 3.85 32.0 In all cases the three components A, B and C were mixed and allowed to rise freely to produce a foam product. The weight proportions of the three components are set forth in ~20 the following table along with product density values, closed cell content and oxygen index values for selected samples. In all cases a thermoset foam product was generated.

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107~9S0 PROPERTIES OF FOAM PRODUCTS
%

COMPONENT COMPONENT COMPONENT DENSITY CLOSED OXYGEN
SPECIMEN A B C P.c.f. CELL INDEX
I 11.9 42.745.4(a) 4.2 25.1 29.0 II 26.04 66.967.0(b) low III 41.0 52.07.0(b) 1.5 __ 26.7 IV 24.0 61.015.0(b)lery __ V 20.0 50.030-0(b)flirly __ __ 10 VI(e) 17.0 43.040.0(b) -- __ __ VII(f) 14.0 36.050.0(b) -- -- --VIII(f) 10.0 25.065.0(b) -- -- --IX 31.0 39.030.0(b) -- -- --X(g) 7.35 27.765.0(a) 8.0 36.7 38 XI 26.04 66.967.0(c)0.76 -- --XII 26.04 66.967.0(d)0.65 -- --XIII 24.0 61.015.0(c) -- -- --XIV 24.0 61.015.0(d)0.80 -- --XV(h) 20.0 50.030.0(c) -- -- --20XVI(h) 20.0 50.030.0(d) -- __ __ XVII(h) 17.0 43.040.0(d) -- -- --Notes (e) - Reaction very fast, difficult to obtain meaningful sample for tests (f) - Rapid reaction, difficult to mix components (g) - 0.22% by weight dibutyl tin dilaurate added as catalyst j (h) - A silica gel forms within a few seconds after mixing \, .

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Example 21 Attempts to manufacture the present foam products using polyether polyols have met with limited success. A
foam was attempted which employs as Component A
7.15 parts by weight of a polyol known as RS-530, which is an alkylene oxide adduct of sucrose having a hydroxyl number of 530;
0.25 parts by weight of a blend of triethylene diamine and dimethyl ethanol amine as a L0 catalyst; and 1.00 parts by weight of fluorotrichloromethane as a blowing agent.

8.40 parts by weight of the described Component A were com-bined with 40 parts by weight of Component B as described L5 in Example 20 and 44 parts by weight of aqueous sodium silicate (STAR). The ingredients did not mix well princi-pally because of the high viscosity of Component A. In an - effort to supply a polyether polyol with a lower viscosity PEP-450 was selected. PEP-450 is an alkylene oxide adduct ~0 of pentaerythritol having a hydroxyl value of 560. Component A accordingly consisted of 7.15 parts by weight PEP-450;
0.25 parts by weight of a blend of triethylene diamine and dimethyl ethanol amine as a catalyst and 3.00 parts by weight of fluorotrichloromethane as a blowing agent. 10.4 parts ~5 by weight of the described Component A were combined with r~ ~e~ -41-1o74gcio 40.1 parts by weight of the Component B (as in Example 20) and 44 parts by weight of commercially available aqueous sodium silicate (STAR). The ingredients mixed adequately and foamed with a slight rise.
Example 22 A foam was prepared employing a polymeric isocyanate (distinguished from a prepolymer) as the source of iso-cyanate groups in Component B. Component A was the same as in Example 20. Component B contained 29.39 parts by !O weight of crude polymethylene, polyphenylene polyisocyanate;
5.43 parts by weight of Phosgard C-22R, a flame retardant additive; 2.20 parts by weight of a silicone fluid; and 5.20 parts by weight of fluorotrichloromethane. Component C was commercially available sodium silicate having a ratio L5 of SiO2/Na20 of 37.1. In order to produce the foam, 11.2 parts by weight of Component A; 44.5 parts by weight Com-ponent B; 42.5 parts by weight Component C and 1.8 parts by weight additional fluorotrichloromethane were combined and mixed for 10 seconds before being poured into a heated mold at 100F, A thermoset foam structure was generated.
ExamPle 23 A foam was prepared employing a non-halogenated saturated polyester resin as the polyol ingredient. Specifically a polyester resin was prepared from adipic acid, trimethylol ~5 propane and diethylene glycol coo~ed to a final acid value . . .

107495~

of about 3.0 and a final hydroxyl value of about 400.
Component A was prepared by combining 11.51 parts by weight of the described saturated polyester with 3.00 parts by we-ght fluorotrichloromethane, 0.25 parts by S weight of a blend of triethylene diamine and dimethyl ethanol amine as a catalyst and 1.00 parts by weight of a silicone fluid as a surfactant.
Component B was the same as that described in Exa~ple 20. Component C was aqueous sodium silicate (STAR).
L0 A foam was prepared by combining 11.6 parts by weight of Component A, 43.3 parts by weight Component B, 43.2 parts by weight Component C and 1.8 parts by weight of a~ditional fluorotrichloromethane. The ingredients were mixed for 10 seconds and poured into a heated mold at about L5 60C. A satisfactory thermoset foam was developed.
ExamPle 24 ; A foam was prepared using as the polyol ingredient a mixture of saturated polyesters and polyether polyols, Component A was a mixture of the Component A described in ~ Example 23 and the following polyether portion containing 11.51 parts by weight RS-530~ which is an alkylene oxide adduct of sucrose having a hydroxyl number of 530; 3,00 parts by weight fluorotrichloromethane; 0.25 parts by weight of a blend of triethylene diamine and dimethyl ethanol amine and 1.00 parts by weight of a silicone fluid. In order to ~ ~r~e~k _43_ produce Component A, 15.9 parts by weight of the polyether polyol portion were combined with 13.0 parts by weight of the polyester of Example 23. The total Component A con-tained 28.9 parts by weight. To this composition was '5 added 108.5 parts by weight of Component B as in Example 20, 108~l parts by weight of Component C (aqueous sodium silicate, STAR), and 4.6 parts by weight supplemental fluorotrichloromethane. The mixture formed a coarse, soft foam.
L0 Example 25 A foam product was prepared employing a glycol as the polyol ingredient. Component A included 5.00 parts by weight of dipropylene glycol, 3.00 parts by weight fluoro-trichloromethane, 0.25 parts by weight of a blend of tri-L5 ethylene diamine and dimethyl ethanol amine as a catalyst and l.00 parts by weight of a silicone fluid surfactant.
Component B and Component C were the same as in Example 20.
A foam was prepared by combining lO parts by weight of the described Component A with 43 parts by weight of Component B and 47 parts by weight Component C. The resulting materials produced a foam mass that exhibited some shrinkage after formation.
Example 26 A foam was prepared employing formaldehyde alone as a modifying additive. Components B and C were the same as :
, described in Example 20. Component A included 10.14 parts by weight of a polyester resin of Example 20, 1.34 parts by weight of formalin (37% solution of formaldehyde in water) and 0.27 parts by weight of a blend of triethylene diamine and dimethyl ethanol amine as a catalyst.
A foam was prepared by combining 11.8 parts by weight Component A, 44.1 parts by weight each of Components B and C. The materials were mixed for 14 seconds. The mixture creamed in 20 seconds and had a rise time of 80 seconds.
`.0 The foam had a compressive strength parallel to the rise of 38.8 psi and an oxygen index of 31.1, ExamPle 27 A foam was prepared employing phenolic resins as a reinforcing resin. The specific resin was an alkali-L5 ~ catalyzed, water-soluble phenol-formaldehyde resin, N-1320 man~factured by Pacific Resins and Chemicals containing 63% by weight nonvolatile material in water. The material is commercially available for normal use as a low ash binder resin. Components B and C were the same as in Example 20.
Component A was prepared by combining 9.45 parts by weight of the saturated polyester resin of Example 20, 2.06 parts by weight of the aqueous phenolic resin N-1320 and 0.24 parts by weight of the blend catalyst, triethylene diamine and dimethyl ethalol amine. The foam was prepared by com-bining 11.8 parts of the described Component A and 44.1 parts by weight each of Components B and C. The resulting foam appeared to shrink after formation. The foam exhibited an oxygen index of 29.8.
Only srall quantities of the aqueous phenolic resins can be employed since the phenolic resins tend to form silica gels instantaneously when mixed with aqueous sodium silicate.
Additional useful polyurethane foam products have been prepared utilizing aqueous potassium silicate having a weight ratio of SiO2/K20 of 2.1 (38.8 weight percent solids) and of 2.2 (29 weight percent solids). The foaming formulations included 17.5, 30, 35 and 50 weight percent of the aqueous potassium silicate component.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A polyurethane foam forming formulation having a viscosity of 1000 to 2000 centipoises comprising:
A. Hydroxyl-terminated polyesters;
B. Essentially anhydrous organic polyisocyanate selected from the class consisting of (1) Polymeric polyisocyanate having a molecular weight greater than 250;
(2) Polyisocyanate prepolymer;
(3) Polyisocyanate quasi-prepolymer;
C. Aqueous sodium silicate having a ratio of SiO2/Na2O
from 2.4 to 3.25;
D. Blowing agent;
E. A surfactant;
F. A catalyst for the reaction of -OH and -NCO radicals wherein the weight of aqueous sodium silicate constitutes from 10 to 60 percent of the total weight of the formulation.

2. The polyurethane foam forming formulation of Claim 1 including 0.5 to 5.0 percent by weight of an organic condensable resin selected from the class consisting of melamine-formaldehyde, melamine-urea and methylolated melamine-formaldehyde; and also including a catalyst for the condensation of melamine resins.

3. The polyurethane foam forming formulation of Claim 1 including 0.5 to 2.0 percent by weight of a phenolic resin.

4. The polyurethane foam forming formulation of Claim 1 including 0.1 to 5.0 percent by weight of formalde-hyde.

5. The polyurethane foam forming formulation of Claim 1 wherein the said blowing agent is halogenated hydrocarbon.

6. A process for producing a rigid foam structure having a density of 2 to 40 pounds per cubic foot which comprises reacting together:
A. A hydroxy-terminated polyester;
B. An organic polyisocyanate; and C. Aqueous sodium silicate having a weight ratio of SiO2/Na2O from 2.4 to 3.25;
wherein at least one of the three components (A, B, C) contains dissolved blowing agent;
in the presence of surfactant and a catalyst for the reaction of -OH and -N=C=O radicals; and wherein the weight of the said aqueous sodium silicate constitutes from 10 to 60 percent of the weight of the components.

7. The process of Claim 6 which comprises reacting the three said components A, B, C wherein the said surfactant is included in A or B, the said blowing agent is included in A
or B, and the said catalyst is included in A.

8. The process of Claim 6 wherein the said blowing agent is a halogenated hydrocarbon.

9. A polyurethane foam forming formulation of claim 6 wherein the said organic polyisocyanate is a prepolymer of an organic polyisocyanate and a polyol.

10. A homogeneous polyurethane foam, essentially free of uncombined water and formed by the process of claim 6, containing silica uniformly dispersed throughout the mass of foam and also containing 5 to 15 percent by weight of a complex salt NA2CO3 . NaHCO3 . 2H2O
uniformly dispersed throughout the mass of foam.