CA1135010A

CA1135010A - Curable pigmented silicate compositions

Info

Publication number: CA1135010A
Application number: CA000356247A
Authority: CA
Inventors: Jerome A. Seiner; John E. Blasko; William G. Boberski
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1979-09-10
Filing date: 1980-07-15
Publication date: 1982-11-09
Also published as: GB2061309B; IT8024551A0; AU520693B2; GB2061309A; DE3033282A1; IT1132715B; JPS5643359A; FR2464978B1; FR2464978A1; JPS591752B2; AU5971580A

Abstract

Abstract of the Disclosure This invention relates to pigmented curable silicate compositions having better pigment dispersions as evidenced by improved color uniformity, hiding power, lower viscosity and consistency. The curable coating composition having improved pigment dispersion, consisting essentially of:
(a) an aqueous phase of (i) from about 2 percent to about 50 percent of a water-soluble alkali metal silicate glass having a SiO2:M20 mole ratio of about 2:1 to about 4:1 wherein M represents the alkali metal;
(ii) from about 0.01 percent to about 5 percent of a water-soluble base having a basicity greater than that of the silicate glass; and (iii) from about 50 percent to about 98 percent of water;
(b) pigment, wherein the pigment represents from about 5 percent to about 90 percent by volume of the solids in the composi-tion; and (c) a water-soluble latent insolubilizing agent for the silicate.

Description

11;~501V

UI~BLE PIG~ENTED SII.ICATE COMPOSITIONS

Background oE the Invention During the past several years, environmental pollution concerns have led those active in the coatings, castings and moldings arts to develop various curabie compositions in which organic solvents derived from petroleum have been eliminated or at least substantially minimized.
Thus, compositions such as water-based compositions and high solids compositions have been extenslvely investigated. Even more recently the high cost and scarcity of petroLeum by-products has engendered interest in the development of curable compositions which are composed entirely of~
or at least substantially of, inorganic components.
Inorganic coating compositions based on alkali metal silicates are well known in the art. Such compositions can be applied from an aqueous medium alone or in combination with various known insolubilizing agents. The insolubilizing agents aid in the fast formation of a water-resistant silicate coating. The coatings are inorganic in nature with the consequent advantages discussed above and possess a desired set of properties.
Unfortunately, pigmented coatings based on the alkali metal silicate can have a less than desired appearance due to an inade-quate pigment dispersion in the coating composition. This inadequate pigment dispersion is most noticeable in lapped areas, where Eresh addi-tional coating composition is applied over a first coat of the same composi-tion.
The present invention relates to pigmented inorganic coatin~
compositions based on water-soluble or water-dispersible silicates which are capable of providing coatings having good color uniforrnity.

1 1;~5 0 1 0 As ~Ised hcrein, al~ percents and ratios are by weLght unless otherwise indlcated.
Summary of the Invention Curable aqueous compositions consist essentially of inorganic constituents. More particularly, the curable compositions consist essen-tially of aqueous solutions or dispersions of silicate glass, pigments and a base having a basicity greater than tha~ of the silicate glass. In one embodiment of the invention, the base is initially ground with the pigment and the resultant grind then combined with the silicate glass.
This technique of mixing minimizes shock.
The invention thus provides a curable coating composition having improved pigment dispersion, consisting essentially of (a) an aqueous phase of (i) from about 2 percent to about 50 percent of a water-soluble alkali metal silicate glass having a SiO2:M20 mole ratio of about 2:1 to about 4:1 wherein M represents the alkali metal;
(ii) from about 0.01 percent to about 5 percent of a water-soluble base having a basicity greater than that of the silicate glass; and (iii) from about 50 percent to about 98 percent of water;
(b) pigment, wherein the pigment represents from about 5 percent to about 90 percent by volume of the solids in the composi-tion; and (c) a water-soluble latent insolubillzing agent for the silicate.
Description of the Invention This invention is concerned with the discovery that the presence of certain bases either preadsorbed on a plgment's surface or separately added to compositions containing the pigment and an alkali metal silicate glass, improve the appearance of cured films formed from the compositions. In a preferred embodiment the compositions also contain metal ion containing latent insolubiliæing agents. The compositions consist essentially of an

2 -~.

. . .

1,1;~5~0 aqueous phase ancl plgment. ~ach o~ the components of the compositions and thecomposit~ons~ method of production are describcd in the paragraphs which follow.

- 2~ -5~0 Watcr-~oluble or wa~er-disper;ible silicate. which are ernployed in the co~npositiolls are the alkali metal siLicates, e.g., sodiu;n silicate, potassium silicate, lithium silicate, and mixtures thereof. Preferred water-soluble silicate glasses are sodium and potassium silicate with SiO~:?t2o mole ratios o~ about 2:l to about 4:l, with U representing al'~ali rnetal. The level of silicate glass in the aqueous phase of the compositions ranges from about 2 percent to about 50 percent, preEerably about lO percent to about 40 percent. (While silicates comrnercially available are usually aqueous solutions of silicate, the afore~entioned percents are given on a silicate solids basis.) The compositions of the invention also consist essentially of at least one pigment. Preferred pigments are characterized by their ability to adsorb a base from an aqueous solution thereof. Many pigrnents displaying this characteristic are useful in the compositions of this invention.
While the term "adsorb" is employed, it is employed in the sense of removal from solution and is not intended to imply a physical rather than chemical interaction between pigment surface and the base. In fact, the precise mode of interaction is not known. It is believed that any pigment having metal ions on its surface capable of interacting with the base can be enhanced by this invention. This includes most commonly employed pigments.
While the invention enhances the coLor uniformity properties of any pigment, particularly useful pigments include titanium dioxide, barium metaborate, alumina, zinc oxide, clay and mica. The invention ~ is particularly useful where the compositions coneain one or rnore organic or inorganic coloring pigrnents which impart a color ~other than white), particularly a pastel, bright or intense color. Useful coloring pigments 11;~50~

include iron o~ide red, bariu-n yello-J, ~inc yellow, zinc green, cadmium yelLow, chrome ~-~ide green, coba~t blue, greell or violet, various rnixed metal oxides and organic pigments of the azo series. Base-treated pigrnents are also useful and can, in part or in full, provide the source of the base discussed below. The pigments are employed as dispersed pulverulent solids. Mi~tures of pigmellts can and generally are employed. The pigments are present in an amount of about 5 percent to about 90 perc~nt and prefera-bly about 30 percent to about 70 percent based on the total volune of solids in the composition, i.e., % PVC.
Another essential con:ponent of the compositions of the inven~ion --is a base having a basicity greater than that of the silicate glass. Such bases include the alkali metai and quaternary ammonium hydroxides, e.g., potassium hydroxide, sodium hydroxide and tetraethyl ammonium hydroxide;
alkali metal silicates having a SiO2:~l20 mole ratio of from about 1:2 to about 2:1 where ~ is alkali metal, e.g., sodium orthosilicate; organo silanolates, e.g., tripotassium -aminopropylsilantriolate, tripotassium N-( -aminoethyl)- -aminopropylsilantriolate, tripotassium -aminopropyl-silantriolate, dipotassium -aminopropylmethylsilantriolate, potassium -aminobutyldimethylsilantriolate, tripotassium methyl-silantriolate, dipotassium dimethylsilandiolate and potassium trimethylsilanolate; and-mi~tures thereof.
The base employed has a basicity grea~er than that oE the silicate glass as measured by their respective p~l's at the same normality. This results in the compositions having a better dispersion as evidenced by , better color unifornity, hiding power, lo~er viscosity and consistency, and being substantially lump-free. The level of base in the aqueous phase of the compositions ranges from abou, 0.01 perc~nt to about 5 percent. A

~ 50~0 preferrcd range of base for dilute applicacions such 3S Eound in eLectrode deposition coating is from about 0.01 percent to about 4 percent. A
preferred can~e oE base in the co~positions for other coating applications ran,es from about 0.1 percent to about 4 percent. An increase in pH in the vicinity of the surface of the pigment is theorized as bPing responsible for the compositions' better pigment dispersions. This increase in pH is bel;eved to be due to the base having a greater affinity Eor the pigmenc's ~urface than the silicate glass.
Bases above described can be added directly as a component of the curable compositions during or after their formulation. Alternatively, the base can be admixed with at least a portion of the pigment to be employed in the composition. ~his l~ter method of incorporating the base into che CompoQitions is preferred; i~ has been found the resultant compositions are even ~ore substantially lump-free due to less shock when the pigmen~/
base and silicate are combined to form the coating compositions.
The compositions are ~ater based. While the amount of water can ~ary widely tepending ~n intended use> generally the aqueous phase Oe the composieions consists essentially of between about 50 percent and about 98 percent water, preEerably between about 60 percent and about 90 percent.
A preferred e~bodi~ent of the invention are the above described compositions additionally consisting essentially of a water-soluble latent insolubilizing agent. Such agents improve the water-resistance of the silicate coatings and are Eor this reason desired. Satisfactory insolu-bilizing agents are described in tl~e following paragraphs.
25 I Metallate insolubilizing agents are describ~d in U.S. Pa~ent No.
4,140,535, issued February 20, 1979 and No. 4,169,735, issued on October 2~ 1~79.

1~35010 The described systems comprise a blend ~f silicates and water-soluble metallate latent lnsolubilizlng agents where the water-soluble latent in-solubilizing agent is selected from alkali metal or quaternary ammonium zincates and borates. Still another water-soluble latent insolubllizing agent is an alkali metal or quaternary ammonium aluminate. Illustrative of such metallate latent insolubilizing agents which can be employed are lithium zincate, potassium zincate, and sodium zincate; lithium borate, potassium metaborate, and sodium tetraborate; and lithium aluminate, potassium aluminate, and sodium aluminate. The term "borate" as used in connection with the alkali metal borates is intended to include ortho-borates, pyroborates, metaborates and more complex borate ions. The alkali metal aluminates, especially sodium aluminate, are preferred in-solubilizing agents.
U.S. Patent 3,715,224, to Campbell discloses solutions and/or colloidal suspensions of water-soluble silicates containing monovalent and divalent metal ion complexes. The disclosed metal ion complexes are useful latent insolubillzing agents here also.
Yet other insolubilizing agents are described in U.S. Patent 4,137,087, issued January 30, 1979. Water-soluble latent insolubilizing agents are formed from metal ions selected from the group consisting of Al , Fe , Cr and Sn and ligands (i.e., complexing agents) selected from the group consisting of ethylenediaminetetraacetate, di-ethylenetriaminepentaacetate, N-~hydroxyethyl)ethylenediaminetetraacetate, nitrilotriacetate ~nd 1,3-propanediaminetetraacetate. It should be noted that other similar or analogous type ligands where they exist may be employed and these are considered to be within the scope of the invention. Illustrative examples of such latent insolubilizing agents are compounds such as sodium ethylene-diaminetetraacetatoaluminate (III), sodium ethyLenediaminetetraacetato-ferrate (III), sodium etllylenediaminetetraacetatochromate (IIIj, and sodium ethylenediaminetetraacetatostannate (II). --~le amount of latent insolubilizing agent included in the compositions can vary considerably depending UpOll desired properties.
Ilowever, in general, ehe amount of latent insolubilizing agent employed is an amount sufficient to enhance wet abrasion and water resistance of the cured composition but which is insufficient to cause an irreversible gel ~-when the uncured composition is stored for 24 hours at 70 C. In most instances, amounts of metallate latent insolubilizing agent ranging from about O.l percent to about 6 percent, preferably from about 0.25 percent to about 2.5 percent by weight, based upon the combined weight of the silicate glass and metallate latent insolubilizing agent are employed.
Insolubilizing agents based on the metal ions and ligands are present at a level of from about 0.2 percent to about 12 percent, preferably from about l percent to about 5 percent, again based on the combined weight of silicate glass and insolubilizing agent.
The reaction between the silicate glass and latent insolubilizing agent is not known with certitude; however, it is theorized the metalLic ion associates with the ligand and the resulting conple.~ maintains the composition in a reasonably stable configuration. Ilowever, upon drying (e.g., air drying or baking) the equilibria shift and the metal ion or the ~ meeallic ion is released to crosslink the silicate glass and form an insoluble silicate composition having e~cellent properties. E~amples of the properties obtained are stain resistance, flame and heat resistance and water resistance.

li;~SO10 The p;gmented curab~e compositiolls o~ the invention can contain ccrtain otller additives such as, ~or example, dyes, ~illers, antioxidants, flow control agents, and surfactants.
In addition it is often advantageous to include in the composi-tions a thickener. Of particular value are water-soluble thickeners which are solub;lized through carboxyl groups. Illustrative of such materials are sodium polyacrylate, potassium polymethacrylate, sodium salts of styrene maleic anllydride copolymers, sodium carboxymethyl cellulose, and potassium polyacrylate copolymers. Also suitable are inorganic thick-eners such as clays and the like. ~
As mentioned above, the curable compositions of the invention can be employed in various applications. The compositions are particularly useful in coatings over a variety of substrates such as wood, metals, glass, wallboard and the like.
The curable compositions can be applied by any conventional ~ethod, including brushing, dipping, rolling, flow coating, roll coating, spraying and the like. Conventional spray techniques and equipment can be utilized.
The curable compositions of the invention can be cured by baking at moderate or elevated temperatures if desired. However, one advantageous property of these curable compositions is that they can be cured by drying in air at ambient temperature without the use of heat. As will be evident, ambient temperature curable compositions are of considerable advantage in that they provide for significant energy savings in comparison to composi-'tions which require elevated temperatures Eor curing.
The examples which ~ollow are illustrative of the invention with composition B of Exa;nple ~Ir repr~senting a preferred embodinent.

1135C)10 EXA~IPL.E I
A coating compositioll is formu1.1ted in the fo11Owing manner.
Twer1ty-five (25.0) grams of a potassium hydroxide solution (40,'. solids) and 56.4 grams water are mixed together. The resultant solution is mixed with 62.0 grams oE titanium dioxide pigment (Titrnox 2060, available from Titanium In~ernational Corp.), 8.0 grams of pigment (Shepherd Green #5, available from Shepherd Chem. Co.) and 33.0 grams of pigment (barium metaborate, avaiLable from Buckman Laboratories as Busan llMl). Coors beads are added to the mixture, followed by a 15 minute grind.
The beads are removed to give a pigment grind having a medium viscosity and little pigment flocculation as evidenced by the presence of only slight "puff" and "hang-up". Puff is defined as being false body, or a high amount of viscosity at low shear rates, that results from pigment flocculation. Hang-up results from the puff. Hang-up is evidenced by paint clinging to the side of a container while paint in the center is being mixed or sheared by the action of the mixer blade. Puff and hang-up are both undesirable.
Next, 350.0 grams of potassium silicate (mole ratio of sio2:~2o = 3.9, 29.1% solids) is added to the pigment grind, follo~ed by 76.0 grams of mica (Micro~ica ClO00, availabLe from English ~ica Corp.), lO.0 grams of --clay (Attagel 40, available from ~inerals and Chemicals Phillipp Corp.), 4.0 grams of sodium carboxymethyl cellulose (available from Hercules Chemical Co. as 12M8 grade) and 3.0 grams of polyethylene oxide (Polyox WS~-205, available from Union Carbide Corp.). This loixture is rnixed for 15 ~rminutes. The final composition is as follows:

~ 1350~

Percent Pot3ssium silicate (solids) 23.23 ~ater 72.89 Potassium hydroxide tsolids) 2.28 Sodium carboxymethyl cellulose 0.92 Polyethylene o~ide 0.68 100. 00 Pigment (53~ PVC) Titanium dioxide 32.81 Shepherd Green #5 4.23 Barium metaborate 17.46 Mica 40.21 Clay 5.29 100 . 00 The composition has a smooth consistency and no puff or hang-up.
The compositions are next coated onto a prepainted plasterboard substrate and evaluated for pigment dispersibility. This is done by first applying a base coat (application made all in one direction), allowing it to dry and then applying a second coat (application made in horizontal and vertical directions to the base coat). A visual evaluation of the coated substrate indicates the coating compositions have good color uni-formity and good lapping characteristics.

E~IPLE II
Co~ting CompositiOnS are formulated to show the e~ect potassium hydroxide has in compositions containing potassiurrl silicate and aluminum ethylenedianine tetraacetate complerc. The compositiolls contain the following components:

11;~501a~

COmDOnellt _ npositions (7 ?
A B C
Potassium siLicate (mvle ratio of SiO2:~20=3.3, solids~ 20.86 20.86 20.86 Water 75.29 74.72 74;14 Aluminum ethylenediamine tetra-acetate complex (solids) 1.80 l.80 1.80 Potassium hydro~ide ~solids) -- 0.57 1.15 Defoa~er ~1) 0.S2 0.52 0.52 Sodium carboxymethyl cellulose (2)1.39 1.39 1.39 Surfactant (3) 0.14 0.14 0.14 i00. 00100 . 00100. 00 55% 54% 53%
Pigment (Z PVC) Titanium dio~ide (4) 56.00 56.00 56.00 Clay (4) 5.33 S.33 5.33 Mica (3~5 ~esh) 38.67 38.67 38.67 100.00 100.00 100.00 (1) Available from Nopco Div. of Diamond Shamrock Cv. as Foamaster ~.*
(2) Available from ilercules Chemical Co. as 7M8S grade.

(3) Available from De~ter Chemical Co. as Strodex PK-90.*

(4) Same as used in ~xample I.
Composition A has noticeable puff~ hang-up and the appearance of a gelatinous structure. Composition B has no puff and a slight, but accepta-ble, hang-up, while Composition C has no puff and very slight hang-up.
Brush application of the compositions to a plasterbvard substrate shows Composition A to exhibit a medium drag during the application.
; The gelatinous structure of the composition (this being an indication of puff) broke do~n on repeated brushings. Compositions B and C exhibit only lo~-medium drag durin~ brush application and the respective paint films show no indication of an objectionable gelatinous structure.

* Trade Mark '~' , ~ ~

50~0 EXA.~PI.~ III
This e~.imple illustrates the use of sodium hydroxide and potassium hydro~ide as base materials in the compositions of the invention. The compositions are made following the procedure of Example I:
Percent A B
Potassium silicate (mole ratio of SiO2:K2o = 3.9, solids) 23.30 23.30 Water 74.05 73.68 Sodium aluminate 0.13 0.13 Sodium hydroxide (solids) 0.91 ---Potassium hydroxide (solids) ~-- l.Z8 Sodium carboxymethyl cellulose (1) 0.92 0.92 Polyethylene oxide (1) 0.69 0.69 lOO.OU 100.00 Pigment (54~ PVC for Compositions A and B) Titanium dioxide (1) 32.80 Shepherd Green ~5 (1~ 4.23 Barium metaborate (L) 17.46 Mica (1) 40.21 Clay (1) 5.29 100 . UO
(1) As used in ~xample I.
Composition ~ is made by first blending 14.6 grams sodium hydroxide solution (27.3% solids), 0.57 grams sodium aluminate and 60.0 grams water.
This blend has added to it 49.0 grams water, 62.0 grams titanium dioxide, 8.0 grans Shepherd Green ~5 pigment and 33.0 grams barium metaborate and is then ~round together wi~h Coors beads for 15 minutes. A poreioll (150.0 gralns) of the potassium siLicate is next added. A~ter removin~ the Coors beads, a 11;~5010 blend of 76.0 grams of mica, 10.0 grams clay, 4.0 grams sodium carboxymethyl cellulose alld 3.0 gr;lms of the surfact.lnt is added. The mixture has next added to it the balance of the potass;um silicate (200.0 grams) to get the finaL coating composition. The composition has only slight puff and no hang-up. -Composition B is made in a similar manner with the substitution of potassium hydroxide for the sodium hydroxide.
The compositions when painted on a substrate in the manner oE
~xanple I and visually tested for color uniforin;ty and lapping proved to be satisfactory. Composition B does have better cure than Com.position ~ as evidenced by B's film having better water-resistance and durability.

E~IPLE IV
This exampie illustrates the advantages of the invention when sodium nethylsiliconate is used as the base material. Two compositions, one being a control, are forrnulated as follows:

Components Cornpositions (%) .
A B
Potassium silicate (mole ratio of sio2:x2o = 3.9, solids) 23.23 23.23 Water 74.26 71.98 Sodium aluminate 0.13 0.13 Potassium hydroxide (solids) 0.11 O.IL
Sodium methylsiliconate (2) -- 2.28 Glycerine 1.14 1.14 Defoamer (1) 0.34 0.34 Sodium carboxymettlyl cellulose (5) 0.68 0 r 68 Thickener (3) O~ll O.Ll 10() . ()01~0 . 00 ~ 50~0 52% 52%
Pir,lnent (% PVC) Titanium dioxide (5) 34.85 34.85 Inoroanic pigment (4) 3.88 3.88 Barium metaborate (5) 18.55 18.55 ~1ica (5) 42.72 42.72 100 . 00 100 . 00 (1) Available from SWS Silicones, Inc. as SWS-214.*
(2) Available from Dow Corr.ing Corp. as Dow Corning 772.*
~3) Available from B. F. Goodrich Chemical Co. as Carbopol 910*-(4) Available from Ferro Chemical Co. as Ferro V3285*

(5) Sa~e as used in Example I
The compositions are made by making a soLution o 0.57 grams sodium aluminate, 0.5 grams potassium hydroxide and 50.0 grams water and blending with additional water (27.3 grams for Composition A and 19.0 ~rams for Composition B), 5.0 gra~s glycerine, and 1.5 grams defoa~ner. Ten (10.0) grams sodium methylsiliconate is added to Composition B. The remaining components ~re added in the following order: 62.0 grams titanium dioxide, 6.9 grams inorganic pigment, 33.0 grams barium metaborate, 3.0 grams C~IC, blended for 10 minutes, 350 grams potassium silicate added under agitation, 76.0 grams mica a~d 0.5 grams thickener and then the total cornposition blended for 10 minutes.
At the end of the blending, Composition ~ exhibited a moderate puff and no hang-up while Composition B exhibited a trace of pufi and no hang-up.
Plasterboard substrates, as in Example I, are next painted with each of ehe compositions. rne color uniformity of the ilm formed by Compo-sition A is very good while that painted with Cornpositioll B is excellent.
Composition A's fiLm has a moderate ~ensity of small lumps of floccul3ted piOment wllile Cornposition B's filln has none.

* Trade Mark - ~4 -:~i3S~

I~ X~ 'L.li: V
Sodium orthosilicate is useci in varyin~ levels in this example to sllow the effect it has on the coating compositions and Eilms rormed therefrom. The compositions are as follows:

Component Compositions (%) A B C D E F
Potassium silicate (mole ratio of SiO2:K20 =
3.9, solids) 23.4723.47 23.47 23.4723.4723.47 Wat-r 73.0172.78 72.55 72.0971.1969.40 Sodium aluminate 0.13 0.13 0.13 0.13 0.13 0.13 Potassium hydroxide (solids) 0.12 0.12 0.12 0.12 0.12 0.12 Sodium orthosilicate pentahydrate -- 0.23 0.46 0.92 1.82 3.61 Citric acid 0 09 0 09 0 09 0 09 0 09 0 09 ~minopropyl propanol 0.23 0.23 0.23 0.23 0.23 0.23 Surfactant (1) 0.97 0.97 0.97 0.97 0.97 0.97 Surfactant (2) 0.14 0.14 0.14 0.14 0.14 0.14 De~oamer (3) 0.23 0.23 0.23 0.23 0.23 0.23 PoLyethylene o~ide (4)0.690.69 0.69 0.69 0.69 0.69 Sodium carboxjmethyl cellulose(4)0.92 0.92 0.92 0.92 0.92 0.92 100.00100.0010().00100.00 100.00 100.00 52% 52% 52% 52% 51~o 50,~
Pi~Jment (~ PVC) Titanium dioxide (4)32.8032.8032.80 32.8032.8032.80 Shepherd Green #5 (4) 4.23 4.23 4.23 4.23 4.23 4.23 Barium metaborate (4) 17.46 17.46 17.4617.4617.46 17.46 Mica (4) 40.2140.21 40.21 40.2140.2140.21 Clay (4) 5.29 5.29 5.29 5.29 _5.29 5.29 10~ 0.00 10U.'~ 100.~0 100.00 100.~0 11;~5010 (1) Noniollic surfactant available froln ~SF-Wyandotte Co. as Tetronic 304. *
~2) Nonionic surfactant available from Rohm & Haas Co. as Triton X4~.*
(3) Available from SWS Silicones, Inc. as SWS-2L4.
~4) Same as used in Example I.
The viscosities of the compositions are measured with a Stormer Yisco;neter and are graded for color uniformity using a scale of 0-100 wi~h 0 being the poorest and 100 being the best. Ihe gelatinous structure is visually estimated as noted. --Composition Viscosity Color Uniformity Gelatinous (Krebs units) Ratinv Structure _ _ A 106 27 slight-moderate E~ 105 42 " "
C 102 33 slight D 97 38 "
E 83 67 none F 82 98 "

The above tests indicate increasing the level of sodium ortho-silicate decreases the viscosi~y, improves color uniformity and reduces ehe formation of an objectionable gelatinous structure in the compositions.

Example VI
This example shows the advantage o~ mi~ing pigment and base together prior to combining with silicate binder. Two compositions ~re formulated. Each has the following composition:

* Trade Mark ' '~',-. . .

il;~50~0 Percent Potassium silicate (molar ratio of SiO2:~2O = 3.9, solids) 23.79 Water 70.16 Sodium aluminate 0.13 Potassium hydroxide (solids) 0.12 Sodium methylsiliconate (1) 2.90 Glycerine 1.17 Defoamer (1) 0.35 Aminomethyl propanol 0.28 - _ Citric acid 0.12 Nonionic surfactant (2) 0.16 Sodium carboxymethyl cellulose 0.70 Thickener (1) 0.12 100.00 - -Pigment (55% PVC) Titanium dioxide (1) 39.75 Shepherd #125 Blue (3) 4.42 Barium metaborate (1) 14.74 Mica (1) 41.09 ioo. oo (1) Same as used in Example IV.
(2) Available from Rohm & Haas Co. as Triton X45.
(3) Available from Shepllerd Chemical Co.
One composition is made by blending the (a) sodium methylsili- -conate with the water, sodium aluminate, potassium hydroxide, glycerine, defoamer, aminomethyl propanol, citric acid and nonionic surfactant with (b) pigments and then combining the blend with the remaining components.
No hang-up or puff is observed at any stage of the formulatioil making;
the composition has a smootn consistency at all stages.

11350~0 A second compos;tion is made iderltical to the first with the e~ception being the post aclditioll of the sodiu[D methylsiliconate to a blend oE all the other remaining co~mponents, Eollowed by agita~ion. rhe final compositioll has a smooth non-gelatinous consistency, free of puff and hang-up; however, heavy puEE and hang-up are noticed in the composition pr_or to the addition of the siliconate. This ilLustrates the advanta~e of adding the base to the pigment prior to combining with silicate.
rhe above examples illustrate the advantages obtained from the present invention. rne examples all show that the inclusion of a base in a silicate-containing composition improves the appearances of resultant -coatings.

Claims

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

1. A curable coating composition having improved pigment dispersion, consisting essentially of:
(a) an aqueous phase of (i) from about 2 percent to about 50 percent of a water-soluble alkali metal silicate glass having a Sammy mole ratio of about 2:1 to about 4:1 wherein M represents the alkali metal;
(ii) from about 0.01 percent to about 5 percent of a water-soluble base having a basicity greater than that of the silicate glass; and (iii) from about 50 percent to about 98 percent of water;

(b) pigment, wherein the pigment represents from about 5 percent to about 90 percent by volume of the solids in the composition; and (c) a water-soluble latent insolubilizing agent for the silicate.

2. The composition of Claim 1 wherein the pigment and base are mixed prior to combining with the silicate glass.

3. The composition of Claims 1 or 2 wherein the level of the base ranges from about 0.01 percent to about 4 percent.

4. The composition of Claim 1 wherein the base is present at a level ranging from about 0.1 percent to about 4 percent.

5. The composition of claim 4 wherein the base is an alkali metal or quaternary ammonium hydroxide, an alkali metal silicate having an Sio2:M20 mole ratio of from about 1:2 to about 2:1 M is alkali metal, an organosilanolate, or mixture thereof.

6. The composition of Claim 5 wherein the base is sodium or potassium hydroxide.

7. The composition of Claim 1 wherein the water-soluble latent insolubilizing agent for the silicate is present in an amount sufficient to enhance the wet-abrasion resistance of a cured coating, but insufficient to cause an irreversible gel when the composition is aged for 24 hours at 70°c.

8. The composition of Claim 7 wherein the insolubilizing agent is a metallate and ranges from about 0.1 percent to about 6 percent by weight based on the combined weight of the silicate glass and insol-ubilizing agent.

9. A composition as in Claim 8 where the latent insolubilizing agent is an alkali metal or quaternary ammonium zincate, aluninate or borate or a mixture thereof.

10. The composition of Claim 7 wherein the latent insolubilizing agent is formed from Al+++, Fe+++, Cr+++ or Sn++ ions and selected from the group consisting of ethylenediaminetetraacetate, diethylene-triaminepentaacetate, N-(hydroxyethyl)-ethylenediaminetriacetate, nitrilocri-acetate and 1,3-propanediaminetetraacetate and is present at a level ranging from about 0.2 percent to about 12 percent based on the combined weight of the silicate glass and insolubilizing agent.

11. The composition of Claim 1 wherein the base is ground with the pigment and insolubilizing agent first and thereafter combined with the silicate glass.

12. The composition of Claim 11 wherein the insolubilizing agent is an alkali metal or quaternary ammonium aluminate.

13. The composition of Claim 12 wherein the silicate glass is alkali metal silicate and the insolubilizing agent is sodium aluminate.

14. The composition of Claim l wherein the aqueous phase consists essentially of (i) from about 10 percent to about 40 percent of the silicate glass, (ii) from about 0.1 percent co about 4 percent of the base and (iii) from about 60 percent to about 90 percent of the water.

15. The composition of Claim 14 wherein the pigment represents from about 30 percent to about 70 percent by volume of the solids in the composition.