CA1163402A - Curable silicate compositions containing condensed phosphate hardeners and ph controlling bases - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Disclosed is a curable composition consisting essentially of (a) from about 10 to about 32 percent by weight of a water-soluble and/or water dispersible alkali metal silicate: and (b) from about 2 to about 10 percent by weight of a metal condensed phosphate hardener in the form of an aqueous dispersion containing a water-soluble base in an amount such that the pH of the aqueous dispersion of the hardener is greater than 9.5.
Also disclosed is a method of preparing such a curable composition.

Description

~ 1 6340~

CURABLE SILI~ATE COMPOSITIONS CONTAINING
CONDENSED PHOSPHATE HARDENERS AND pH CO~TRGLLING BASES

Environmental pollution concerns have led those in the coatings and resins arts to develop curable compositions from which organic petro-leum based solvenes have been eliminated or at least ~ubstantially reduced.
Additionally, the high cost and scar~ity of petroleum by-products has gen- -erated interest in the development of curable compositions based entirely, or at least substantislly, on inorganic components.
Inorganic coating compositions based on alkali metal silicates and inorganic phosphate hardener~ sre known. However, ~hen alkali metal silicates and inorganic phosphate hardener~ are mixed, they tend to rapidly coagulate, solidify or the like due to th~ strong reactivity between the silicate and the pho~phate. The particles or small lumps fonned in these alkali silicate/phosphate hardener compositions, due to this tendency toward prematurely rapid reaction are undesirable, for example, in applications employing spraying techniques. Addieionally~ cured coatings produced fron compo~itions containing such particles contain undesirable lumps.
A method is described in ll S Patent 3,930,876 directed to pre-venting the rapid reaction of the silicate with the phosphate to increase pot life wherein a condensed phosphate hardener prepared using double-oxides having the "spinel" structure i9 pretreated with 8 silicate or a modified silieate to form a slurry or paste having a pH of 5 to 9.5, preferably 6 to 8.5. The pr9cedure described therein requires that the condensed phosphate hardener be prepared using a double oxide having a "spinel" ~tructure. Ih8 pretreatment of the hardener described in U.S. patent 3,930,876 generally i 3 ~3~02 1 takes from 10 to 30 hours and produces an inert coating on the phosphate hardener containing no free acid rendering it less reactive.
The present invention i9 directed to curable inorganic coating compositions based on water-soluble and/or water-dispersible alkali metal silicstes which are relatively storagP stable, essentially lump-free, easily sprayable, and curable at relatively low temperatures to smooth, essen-tially lump-free, durable coatings which are resistant to high temperatures, water, detergents snd cracking. The invention is also direceed to a method for ?roducing the compositions of the invention and to a method of forming coatings from the compositions. Coatings produced from the compositions of the invention are suitable for use, for example, as a replacement for por-celain in appliances. It is notable that coatings prepared from the compo-sitions of the present invention are substantially less energy intensive than porcelain coatings and essentially lump free as compared to coatings prepared from aqueous silicate/condensed phosphate hardener compositions ~enerally known in the art.

SUMMARY 0~ THE INVENTION
The aqueous compositions of the present invention substantially comprise inorganic constituents. They are aqueous materials comprising a specified amount of an aqueous alkali metal silicate and a specified amount of an aqueous dispersion of a metal condensed pho6phate hardener containing a water-soluble base such that the pH of the dispersion is greater than 9.5 and typically at least 10. The compositions are produced by mixing the aqueous silicate with the aqueous dispersion of the metal condensed pho3-phate hardener for which the pH has been adjusted to greater than 9.5 with the water soluble base. m e pH adjustment of the dispersion of the condensed l phosphate hardener minimizes shock (i.e.. the formation of undesirable particles or lu~p9) in the compositions of the invention. The compositions additionally may contain a pigment, a filler, various addieives and mix-tures thereof.

DET ILED _ S_ IPTION OF T~E INVENTION
The present invention comprises an aqueous curable composition consisting esseneially of (A) from about 10 to about 32 percent by weight of a water-soluble and/or water-dispersible alkali metal silicate: and (B3 from about 2.0 to about lO percent by weight of a metAl condensed phosphate hardener in the form of an aqueous dispersion containing a water soluble base. The amount of base in the dispersion of hardener is sufficient to raise the pH of the hardener dispersion to greater thsn 9.5, typically to at least 10. m e ability to include such hi8h levels of base in the hardener dispersions in the present compositions iB indeed surprising considering the generally known adverse effects that high levels of ba3e typically have on properties of ~ilicate-based coatings such as water resistance and resistance to blistering. Yet the compositions of the present invention cure to smooth essentially lump-free, durable coatings having excellent water, detergent, heat and cracking resistance.

Water~soluble and/or water-dispersible alkali metal silicates (component A), which may be used in the compositions of the invention, include, for example, sodium silicate, pota~sium silicate and lithium silicate. Preferred aqueous silicate6 for component A include solutions and/or dispersions, preferably solutions, of sodiuM and/or potassium sili-cates, commonly referred to as waterglas~es. Potassium ~ilicate waterglass is particularly preferred. m e water-soluble and/or water-dispersible i 1 63402 1 alkali metal silicates suitable for the present invention have a SiO2:M2o mole ratio generslly ranging from about 2.0:1.0 to about 4~0:1.0, preferably from about 3.3 1.0 to about 3.5-1.0, wherein M represents the alkali metal.
The amount of silic2te glass solids (from component A) in the compositions of the invention generally ranges from about 10 to about 32 percent by weighe, preferably from about 15 to about 25 percent by weight.
Although the above alkali metal silicates are preferred, water-soluble and/or water-dispersible alkali metal silicates which have been modified with an oxide or an hydroxide of a metal such a~ Al, Ca, Mg, Zr~
V, Zn or Cs may al~o be used as component A. Oxide- or hydroxide-modified ~ilicates may be obtained, for example, by mixing an aqueous ~olution of the appropriate metal oxide or metal hydroxide with the aqueous silicate and heating the mixture while stirring. Usually, the heating i9 conducted at about 50 to 100C for about 1 to 72 hours. However, if the reaction is conducted in a pressure vessel at a temperature higher than 100C, the reaction time may be shorter. The amount of the oxide or hydroxide may be 0.5 to 3.0 parts by weight per 100 parts by weight (based on dry solids without water of crystallization) of the silicate.
The metal condensed phosphate hardener may be any such hardener generally known for use in silicate-based inorganic paints or coating com-pO8 itions. The metal condensed phosphates for such hardener may be pre-pared, for example, by dehydration of one or more ortho phosphates at about 300 to about 1200C. For example, condensed aluminum phosphate msy be pre-pared by evaporating an aqueous 30 percent by ~eight Al(H2P04)3 solution to dryness snd heating the resulting material to a temperature of about 400C
to 500C. Another example of a method of preparation of a condensed aluminum phosphate, described in ~.S. Patent 3,943,231, is to spray-dry a relatively ~ 1 ~3~02 dilute solution or suspension of an aluminum orthophosphate containing - P205 and A1203 in the molar ratio desired in the final product at tempera-tures higher than 250C to effect direct transformation into condensed aluminum phosphates. German Patent 1,252,835 describes a method for obtaining condensed aluminum phosphates wherein an aluminum phosphate solution is evaporated to dryness and the resulting material sub~ected to a two-step heat treatment at different temperatures. Finally, methods for preparing condensed iron phosphates and condensed aluminum phosphates are described in the Bulletin of the Societe Chemique deFrance, article 1~ No, 337~ (1961), pages 2277-2282 and the Bulletin of the Societe Chemique deFrance, article No. 221, (1962), pages 1237-1243.
Metal condensed phosphates used as hardener in the present invention typically comprise condensed aluminum phosphates. Various con-densed aluminum phosphates, including their methods of preparation, are described, for example, by d~Yvoire in the Bulletin of the Societe Chemique deFrance, (1961), article No. 337, at 2277-2282 and the Bulletin of the Societe Chemique deFrance, (1962), article No. 221 at 1237-1243 wherein a cyclic aluminum tetrametaphosphate, (i.e., the A-form of Al(P03)3) and four long-chain polyphosphates (i.e., the B-, C-, D- and E- forms of

2~ Al(P03)3) are identified. As reported by d~Yvoire, these condensed alumi-num phosphates may be produced, for example, by reacting P205 and A1203 in n molar ratio respectively of from 4:1 to 15:1. U.S. Patent 4,216,190 describes a method for making B-form aluminum trimetaphosphate by the nddition of concentrated ammonium hydroxide to a solution of aluminum dihydro~en phosphate, Al(H2P04)3, to effect the formation of a white precipi~ate which is directly converted to the B-form aluminum trimeta-phosphate Al(P03)3 by a single elevated temperature treatment.

" ~ J ' _ S

~ ~ 63~02 1 Condensed aluminum phosphates used as hardener in the present invention preferably comprise B-form sluminum metaphosphate, snd most preferably comprise a mixture of A-form aluminum metaphosphate and B-form sluminum metaphosphate. W~.en a mixture comprising A-, and B-form aluminum metaphos-phates is used as hardener, the weight ratio of the B-form ~o A-form alumi- -num me~aphosphate generally ranges from about 3 5 to sbout 4:1~ preferably from abouc 7:3 to about 4:1.
The amount of metal condensed phosphate hardener solids in compositions of the invention ranges from about 2.0 to about 10 percent by weight based on the total composition. The weight ratio of total alkali metsl silicAte solids to metal condensed phosphate solids, respectively, in compositions of the invention generally ranges from About 1.7:1.0 to about 10.6:1.0, preferably from about 1.9:1.0 to about 2.6:1Ø
The condensed phosphate hardener used in the invention may be pre-pared, for example, by mixing the condensed phosphate with water to form an aqueous dispersion such as a slurry or paste. A water-soluble base is mixed with the aqueous dispersion of condensed phosphate until the pH of the mix-ture is greater than 9.5. preferably at least 10. The composition of the present invention is then formed by mixing the aqueous dispersion of con-densed phosphate (component B) and the water-soluble and/or water-dispersible alkali metal silicate (component A) while the pH of the dispersion of con-densed phosphate i8 at an appropriate value as described previously. Gen-erally, the condensed phosphate dispersion i8 mixed with the water-soluble and/or water-dispersible silicate (component A) within ahout a few minutes from when the pH adjusted disp2rsion of condensed phosphate i9 prepared.
If the pH of the aqueous disper~ion of condensed phosphate (com-ponent B) is too low ju~t prior to mixing with the aqeuous alkali metal silicate (component A), upon mixing, gel particles or lumps tend to occur .

i 1 63402 1 in the composition, and highly undesirable lumps or particles tend to occur in cured coatings produced from the composition.
Bases suitable for raising the pH of the aqueous dispersion of hardener to an appropriate level in the present invention are believed not to form an insoluble coating on the condensed phosphate during the pH
adjustment of the hardener disper~ion.
Examples of bases which may be used to raise the pH of the aque-ous dispersion of condensed phosphate include: alkali metal hydroxides such as sodium hydroxide, potassiu~ hydroxide and lithium hydroxide;
10 quaternary smmonium hydroxides such as tetraethyl ammonium hydroxide and tetraethanol ammonium hydroxide; ammonia; amines such as triethylamine and 3-(diethylamino)-propan-1-ol; tertiary sulfonium hydroxides such as trimethyl sulfonium hydroxide and triethyl sulfonium hydroxide; quaternary phosphonium hydroxides such as tetramethyl phosphonium hydroxide and tetraethyl phosphonium hydroxide; organosilanolAtes such as tripotassium ~-aminopropylsilantriolate, tripotasaium N-(~-aminoethyl) -~-aminopropyl-silantriolate, dipotassium dimethylsilandiolate, potassium trimethylsilanol-ate, bis-tetramethylsmmonium dimethylsilandiolate, bis-tetraethylammonium dimethylsilandiolate, and tetraethylammonium trimethylsilanolate; and mixtures thereof. Of the bases described above, alkali metal hydroxides, quaternary ammonium hydroxides, ammonia and amines are preferred. The alksli metal hydroxides are particularly preferred.
The organosilanolate~, which msy be used as the base to adjust the pH of the aqueous dispersion of condensed phosphate, are known and cor-respond to the formula RnSi(OM)4_n wherein R is an organic radical, M is an alkali metal or a quaternary ammonium radical and n is an integer from 1 to

3. R may be an organic group such as an aliphatic group, a cycloaliphatic i 1 ~3402 1 group, an araliphstic group, an alkenyl group, etc., and R may be ~ubsei-tuted with groups such as amino, mercapto snd/or halogen. ~hen organo-~ilanolates are used as the base to raise the pH of the hardener dispersion, it is preferred to u5e an alkali metal salt of 3-aminopropylsilantriol, an alkali metal salt of dimethylsilandiol and mixtures thereof. It is also preferred to use potassium as the alkali metal in these alkali metal salts.
The base used at the specified levels in the present invention reduces the reactivity of the condensed phosphate hardener for the water-soluble and/or water-dispersible alkali metal silicate, thereby increasing the useful life of the composition and eliminating either completely or sub-stantially shock, i.e., undesirable particle formation between the silicate ~component A) and the condensed phosphate. The useful life of the compo-sitions of the present invention ranges from about 15 to aboue 90 minutes.
As used herein, "useful life" means the period of time the composition remains fluid and essentially free of undesirable particles or lumps such that, for example, a cured coating produced from the composition is essen-tially lump-free. Thus, the use of the base in the specified amount results in compositions having better dispersion characteristics as evidenced by lower viscosity, better sprayability and a consistency which is essentially lump-free. m e percent by weight of the base in the compositions of the invention generally ranges from about 0.2 percent to about 0.8 percent, preferably from about 0.2 percent to about 0.5 percent As discussed pre-viously, the base i9 admixed with the dispersion of condensed phosphate hardener before the condensed phosphate hardener is admixed with the water-soluble and/or water-dispersible alkali metal silicate (component A). The amount of base used is ~ufficient to raise the pH of the aqueous dispersion of condensed phosphate (component B) to greater than 9.5, typically to at ~ 1 63402 1 least 10~ before the hardener dispersion is admixed with the water-soluble and/or water-dispersible alkali metal ~ilicate (component A). The composi-tion of the invention is then formed by combining the hardener dispersion ~nd water-soluble and/or water-disper~ible alkali metal ~ilicate before the pH of the hardener dispersion falls below 9.5, preferably before falling below 10.
If the base is used in amounts appreciably greater than that needed to prevent shock when the hardener dispersion is combined with the water-soluble and/or water-dispersible silicate, the resultant propertiec of coatings formed from the compositions will reflect properties such as 10 decreased water resistance, as one in the art would anticipate from using excessive levels of base. Thus, it is indeed surprising that cured coat-ings produced from the compositions of the present invention in which the pH of the hardener dispersion (component B) i~ raised to such high levels in accordance with the invention, are highly water- and detergent-resistant, in addition to being heat-resistant, crack-resistant and lump free.
The amount of water in the compositions of the invention may vary widely depending on the intended use. Generally, the aqueous phase of the compositions of the invention contains from about 42 percent to about 64 percent by weight water, preferably from about 50 percent to about 60 per-20 cent by weight water.
In a preferred embodiment, the compositions of the inventioninclude st least one pigment. Suitable pigments include those generally ~nown and u~ed in the paint and coatings industry provided that they are stsble at the high pH values of the compositions of the invention and pro-vided they do not precipitate the aqueous alkali metal silicate in the~e compoRitions. It is preferable to use inorganic pigments where composi-tions for high temperature applications are desired. Examples of suitable ~ 3 63~0~

1 pigments include- al~mina ~ydrates~ barium metaborate, ~inc oxide, white and colored pigments based on titsnium dioxide, iron oxide red, iron oxide black, manganese black, and carbon black. The pigments are generally pul-verized solids and mixtures of pigments also may be employed. Particularly preferred pigments include titanium dioxide available as R-900 from E. I.
duPont de Nemours ~ Company, iron oxide, and Shepherd Black #l available from The Shepherd Chemical Company. Pigments may be incorporated at any stage of formulation of the compositions, but preferably are included in the aqueous dispersion of condensed phosphate hardener prios to combining 1~ the hardener with the water-soluble and/or water~dispersible alkali metal silicate (component A).
Compositions of the inven~ion may also include one or more fillers.
Suitable fillers include inert fillers and/or reinforcing fillers generally known in the art provided they are stable at the high pH values of the com-positions of the invention and provided they do not precipitate the silicate in the compositions. Examples of suitable fillers include: silica, mica, clay, bentonite, sand, glass fibers and steel fibers. The fillers may be incorporated at any stage of formulation of the compositions.
Additionally, the compositions of the invention may contain one or more generally known additives. Examples of additives include dyes, defoamers, release agents, &nti-mar agents, flow control agents, surfact-ants, thickeners, fungicides and mildewcides. m ese various additives may be incorporated at any stage in the formulation of the compositions of the invention.
When pigments, fillers, and/or additives, previously described, are included in a composition of the invention, they generally may be used in amounts of about 32 percent to about 80 percent solids, preferably from about 50 percent to about 60 percent solids, based on the total volume of solids present in the composition.

~ 3 ~3~02 1 m e composition~ of the invention have 8 variety of applications.
They are particularly ugeful in coatings, especially where high tempera-ture, water snd detergent resiseance are desired. The compo6itions may be applied to a wide variety of substrates includ;ng, for example, wood, metal, glass, wallboard, cement and the like. They may be applied by any known method including, for example, brushing, dipping, rolling, flow coating, doctor roll coating, 6praying, and the like. Generally known ~pray tech-niques and equipment may be utilized.
The compositions of the invention can be cured ae moderate or 10 elevated temperatures. m ey may be air dried 8~ ambient atmo~pheric tem- -peratures, but the compositions ~o cured are not a8 water resistane and uniform (e.g. with respect to absence of cracking) as when cured by baking at moderate or elevated temperatures. Generally, the compo6itions of the invention can be cured in relatively short period~ of time at temperatures as low as about 100C, typically as low as about 200C9 to form smooth, essentially lump-free, durable heat-,water-, and detergent-re~istant coat-ings. Of course, the curing time will vary depending on the curing tem-perature used.
The following examples illustrate the invention. Amounts and percentages are by weight unless specified otherwiae. When used herein, "pbw" means "parts by weight."

E~AMPLE I
(la) B-form aluminum metaphosphate ant A-form aluminum metsphos-phate in the proportion~ indicated in the following TABLE 1 were ground with enough water to produce each of the aqueou~ ~lurries, herein designated A, B and C, containing the percents by weight ~olids ind;cated in TABLE 1.

~ :1 63~02 B-form Aluminum A-form Aluminum SlurryMetaphosph_te Metophosphate _Solids A 64 36 57.8 B 50 50 56.9 C 34 66 54.9 (lb) Three sluminum met2phosphate harteners, herein designated HA, HB and HC, were prepared by mixing ~lurries A, B and C respectively with the components indicated and in the amounts set foreh in the follo~ing TABLE 2.

Hardener HA Hardener HB Hardener HC
(pbw)(pbw) (pbw) water 145.5141.4 131.8 ~r~ aqueous 50% KTPPl20.0 20.0 20.0 Strodex*PR-902 Strodex~SEK-503 6.2 6.2 6.2 Foamastçr~VL4 2.3 2.3 2.3 Attagel~405 14.0 14.0 14.0 Slurry A 259.5 - --Slurry B -- 263.6 --Slurry C -- -- 273.2 Micromica~C-10006 45.0 45.0 45.0 Minu~ 107 20.0 20.0 20.0 TiO28 104.6104.6 104.6 lA 50% solution of potassium tripolyphosphate.
2A surfactant containing 90Z solids comprising potassium salts of or8ano-phosphate~ available from Dexter Chemical~ Corp.
30 3A surfActant containing 50~ solids comprisin~ potassium salts of organo- -phosphates available f~om Dexter Chemic~ls Corp.
4An antifoaming agent ovailable fro~ Diamond Shamrock Corp.
5A clay additive available from Englehard Minerals Corp.
~ica available from ~nglish Mica Corp.
7A silica extender svail&ble from PGS Corp.
8Titsnium dioxide pig~ent available AS R-900 from E. I. duPont de Nemours Company 1 (lc) 16.2 pbw of sn squeous 50~ potassium hydroxide ~olution was 610wly added to each of the hardener~, ~A. ~B and HC, thereby raising the p~ of each hsrdener to 10.5.
Then, within a few minute6 from when each pH adjusted hardener was prepared, each hardener was mixed ~ith an aqueous alkali silicate composition contsining 43.0 pbw water, 422.4 pbw ~queous sodium silicate (37.9~ solids; mole ratio of SiO2/Na20 ~ 3.40), 360.5 pbw aqueou~ potas-sium silicate (38.8X ~olida: mole ratio of Sio2/X2o ~ 3.30), and 44.6 pbw mica (Micromica C-3000 from English Mica Corporation) to produce three compositions, herein designated CA, CB ~nd CC respecti~ely, which had the characteristics represented in the following TABLE 3.

Composition CA COmpOB it ion CB Composition CC
total % solids 46.8% 46.8Z 46.8%
X silicates (solids) 19.9% 19.9~ l9.9Z
% aluminum metaphosphate 9.95X 9.95Z 9.95%

Weight raeio of B-form to A-form aluminum metaphosphate 64/36 50/50 34/66 (ld) After about 30 ~inutes from preparation, each of the compositions, CA, CB and CC, described above, wa~ sprayed onto a steel psnel to form a lump-free, wet film having ~ thickne~s of about 6 mils.
Each of the panels was cured for 45 minutes at 2207C to produce a ~mooth, lump-free, dry film having a thickness of from 2.5 to 3 mils.
All of the ~oated panels were then ~ubjected to the following tests with the indic~ted reQult~. When subjected to a temperature of 537.8-C for 1 hour, no bli~tering occurred on 8ny of the panels. When soaked in boiling water for 24 hour~, no aoftening or discolor~tion occurred in any of the coatings. When subjected to a 1:1 by weight mixture ~ ~ 634~

1 of vegetable oil to oleic acic at 400C for 8 hours, only very slight ~tsining~ ~hich was hardly noticeable, occurred on the coatings.
(le)(Comparison) A composition was prepared in the same manner 8S composition CA in part ~lc) above except that only enough squeous 50%
potassium hydroxide was added to hardener HA to raise the pH of the hard- -ener to B.5. After about 30 minutes from preparation, this composition was sprayed onto a steel panel to form a wet film having a thickness of about 6 mils. ~umerous undesirable lumps were observed in the wet film. The panel then was cured for 45 minutes at 220~C to produce a dry film having a thicknesR of from 2.5 to 3 mils. Although similar results were obtsined for ~his cured film as compared to coatings prepared frGm compositions CA, CB and CC in EXAMPLE I when sub~ected to the heat, hot water ~oak flnd stain tests, this cured film was permeated with lumps.

EXAMPLE II
(2a) An aluminum metaphosphate hardener in the form of a paste was prepared by milling ehe components indicated in the ~mounts set forth in the following TABLE 4.

(pbw) water 510.0 aqueous 50% RTPP* 40.0 Strodex PK-90* 7.0 Strodex SEK-50* 12.4 Foamaster VL* 4.6 HB hardener** 240.0 A-form alu~inum metaphosphate*~* 60.0 TiO2* 209.2 Minusil-10* 40.0 Micromica C-1000* 90.0 *Described in EXAMPLE 1.

**~n aluminum metaphosphate hsrdener containing ~bout 80X by weight B-form aluminum metaphosphate and about 20Z by weight A-form aluminum metapho~ph~te sv~ilable as HB h~rdener ~rcm Pennwalt Corp.
; ***Available from Rhone-Poulene, Inc, 1 ~1 63402 1 (2b) An aqueous alkali silicate composition was prepared by milling 86.0 pbw water, 721.0 pb~ aqueous potassium silicate (38.B~ ~olid~:
mole ratio of Sio2/R20 ~ 3.30)~ 844.8 pbw aqueous sodium silicate (37.9% solids: mole ratio of SiO2/Na20 ~ 3.40), 29.4 pbw clay (Attagel 40 from Englehard Minerals Corp ), and ~9.2 pbw mica (Micromica C-3000 from English Mica Corp.).
(2c) Three coating compositions herein designated CA, C8~ snd CC respectively were prepared a~ follows.
Three 300 pbw sa~ples of the aluminum metaphosphate hardener of part (2a) above were mixed with sufficient aqueous 50% potassium hydroxide 801ution to raise the pH to 9.0, 9.5 and 10.0 respectively. These three potassium hydroxide treated hardeners will be desi8nated herein HA. ~B, and HC respectively.
Then within a few ~inutes from when each pH adjusted hardener was prepared, each hardener (NA, B , and HC) was mixed with 437.8 pbw of the aqueous alkali silicate composition of part (2b) above to form three coating compositions herein designated respectively CA, CB, and CC.
Coating composition CA prepared from hardener HA contained an undesirable amount of lumps. Coating compositions CB and CC prepared from hardeners HB and HC contained almost no lumps.
Each of the three coating compo3itions (CA, CB, and CC), was sprayed onto six dry steel panels to form three set~ of six psnels e~ch.
The steel panels were all baked et 220-C for 1 hour.
The six cured coatings prepared from coating composition CA for which the pH of the hardener dispersion, HA, had been adjusted to 9.0, were relatively smooth but exhibited extremely poor adhe~ion to the steel substrate at both the edges and the interior face~ of all ~i~ panels as evidenced by severe cracking and peeling.

1 The si~ cured coatings prepared from coating composition CB for which the pH of the hardener dispersion, HB, had been adjusted to 9.5 were relatively smooth but all exhibited exeremely poor gdhesion ~9 evidenced by cracked and peeled edges on all but one of the panels and cracked and peeled interior faces on all six panels.
The six cured coatings prepared from coating composition CC for which the pH of the hardener dispersion, HC, had been 3djusted to 10.0 were all smooth. Only two of the six panels exhibited any cracking or peeling at the edges and these defects were minor. None of these ~ix panels exhibited any crflcking or peeling of the coating at the interior faces.

Claims (27)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An aqueous curable composition consisting essentially of:
(a) from about 10 to about 32 percent by weight of a water-soluble and/or water-dispersible alkali metal silicate and (b) from about 2 to about 10 percent by weight of a metal condensed phosphate hardener in the form of an aqueous dispersion, said aqueous dispersion containing a water-soluble base in an amount such that the pN of said aqueous dispersion of said hardener is greater than 9.5.

2. The composition of Claim 1 wherein said base is in an amount such that the pN of said aqueous dispersion of said hardener is at least 10.

3. The composition of Claim 1 wherein the amount of said sili-cate ranges from about 15 percent to about 25 percent by weight and the amount of said hardener ranges from about 8 percent to about 10 percent by weight.

4. me composition of Claim 3 wherein said base is in an amount such that the pH of said aqueous dispersion of said hardener is at least 10.

5. The composition of Claims 1 or 3 further comprising a pigment, a filler. an additive or a mixture thereof.

6. The composition of Claims 1 wherein said base is selected from the group consisting of an alkali metal hydroxide, ammonia, an amine, a quaternary ammonium hydroxide, a quaternary phosphonium hydroxide, a tertiary sulfonium hydroxide and mixtures thereof.

7. The composition of Claims 1 wherein said base is an organosilanolate or a mixture of organosilanolates.

8. The composition of Claim 6 wherein said base is potassium hydroxide or sodium hydroxide.

9. The composition of Claim 7 wherein said organosilanolate cor-responds to the formula:
RnSi(OM)4-n wherein R is an organic radical, M is an alkali metal or a quaternary ammonium radical and n is an integer from 1 to 3.

10. The composition of Claim 9 wherein said organosilanolate is dipotassium dimethylsilandiolate or an alkali metal salt of 3-aminopropyl-silantriol.

11. The composition of Claim 8 wherein said silicate is 3 water-soluble alkali metal silicate.

12. The composition of Claims 1 wherein said metal condensed phosphate hardener comprises a condensed metal metaphosphate.

13. The composition of Claim 12 wherein said condensed metal metaphosphate is a B-form condensed metal metaphosphate.

14. The composition of Claim 13 wherein said B-form condensed metal metaphosphate is B-form condensed aluminum metaphosphate.

15. The composition of Claim 12 wherein said metal condensed phosphate hardener comprises a mixture of B-form condensed metal meta-phosphate and A-form condensed metal metaphosphate.

16. The composition of Claim 15 wherein said metal condensed phosphate hardener comprises a mixture of B-form condensed aluminum meta-phosphate and A-form condensed aluminum metaphosphate.

17. The composition of Claim 16 wherein said B-form condensed aluminum metaphosphate and said A-form condensed aluminum metaphosphate are in a ratio by weight respectively ranging from about 3:5 to about 4.0:lØ

18. The composition of Claim 11 wherein said water-soluble alkali metal silicate has an Sio2:M2O mole ratio of about 2.0:1.0 to about 4.0:1Ø

19. A method of producing an aqueous curable composition comprising:
(a) mixing from about 10 percent to about 32 per-cent by weight of a water-soluble and/or water-dispersible alkali metal silicate; with (b) from about 2.0 to about in percent by weight of a metal condensed phosphate hardener in the form of an aqueous dispersion, said aqueous dispersion containing a water-soluble base in an amount such that the pH of said aqueous dispersion of said hardener is greater than 9.5.

20. The method of Claim 19 wherein the pH of said aqueous disper-sion of said hardener is at least 10.

21. m e method of Claims 19 wherein said base is selected from the group consisting of an alkali metal hydroxide, ammonia, an amine, a quaternary ammonium hydroxide, a quaternary phosphonium hydroxide, a tertiary sulfonium hydroxide and mixtures thereof.

22. The method of Claims 19 or 20 wherein said base is an organo-silanolate or a mixture of organosilanolates.

23. The method of Claim 21 wherein said silicate is a water-soluble alkali metal silicate having a SiO2:M2O mole ratio ranging from about 2.0:1.0 to about 4.0:1.0 and said metal condensed phosphate hardener comprises a mixture of B-form condensed aluminum metaphosphate and A-form condensed aluminum metaphosphate, the ratio by weight of B-form to A-form condensed aluminum metaphosphate in said mixture ranging from about 3:5 to about 4:1.

24. A method of forming a substantially inorganic coating on a substrate comprising:
(a) applying to said substrate an aqueous coating composition consisting essentially of (i) from about 10 percent to about 32 percent by weight of a water-soluble and/or water-dispersible alkali metal silicate, and (ii) from about 2.0 to about 10 percent by weight of a metal condensed phosphate hardener in the form of an aqueous dis-persion, said aqueous dispersion containing a water-soluble base in an amount such that the pH of said aqueous dispersion of said hardener is greater than 9.5; and (b) curing said coating composition.

25. The method of Claim 24 wherein said metal condensed phosphate hardener comprises a B-form condensed aluminum metaphosphate.

26. The method of Claim 24 wherein said silicate is a water-soluble alkali metal silicate having a SiO2:M20 mole ratio ranging from about 2.0:1.0 to about 4.0:1.0 and said metal condensed phosphate hardener comprises a mixture of B-form condensed aluminum metaphosphate and A-form condensed aluminum metaphosphate, the ratio by weight of B-form to A-form condensed aluminum metaphosphate in said mixture ranging from about 3:5 to about 4:1.

27. The method of Claim 26 wherein the pH of said aqueous dispersion of said hardener is at least 10.