CA1193380A

CA1193380A - Filler of silanated calcium carbonate pre-treated with soluble sodium silicates

Info

Publication number: CA1193380A
Application number: CA000392723A
Authority: CA
Inventors: Ravindra D. Kulkarni; Errol D. Goddard
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1980-12-29
Filing date: 1981-12-18
Publication date: 1985-09-10
Also published as: US4374178A

Abstract

ABSTRACT
This invention relates to a method for producing novel filler compositions to improve the properties of natural and synthetic resins which consist of calcium carbonate, sodium silicate and organosilane coupling agents by pretreating calcium carbonate with soluble sodium silicate, thereby tranforming the silane-unresponsive calcium carbonate into a silane responsive filler.

Description

3~
1~6~5 FILLER OF SIL,~NATED CALCIUM CARBONATE
PRE-TREATED WITH SOLUBLE SODIUM SILIChTES

BACKGROUND OF THE INYENTION

1~ Field of the ~n~ention This invention relate!~ to novel filler compo-sitions comprising calcium ~arbonate, sodium silicate, and organosilane coupling agents~ to processes for preparing said filler composieion~, and to thelr use in polymer composites.

2. Description of the Prior Art I~ has long been known tha~ various particu-late inorganic substances can be used ~s ~illers to ~mprove the ec~nGmical and/or mechanical properties of natural and synthetic resins, It has been known for almost as long tha~ the benefits of siliceous fillers, such as 5ilica~ ~uartz, asbestos, glass, ~nd various cl~ys on the mechanieal properties o polymer compo-qites can be ~ignificantly Pnh~nced by employing organosilane coupling a~ents in addition to the fillers.
Calclum carbonate is a widely available and economlcal (i.e.~ cheap)~ubstance which in par~iculate form would be suitable or ùse as a filler. Howe~er, pre-~um~ly because it t~ not silieeous in nature1 it is not ~ery respons~ve ~o treatmen~ with organo~ilane coupli~g a~ents; wlthout sueh trea~ment~ polymer c~mposites filled ~ith calcium car~nate do Dot show satisactory mechan-lcal pr~pea~ies.

~,', ,~....

~ ~ ~ 3 ~ 126~5 Two approaches have been developed to modify the surfaces o~ nonresponsive fillers such as calcium car~onate. One d~als with the coprecipitation of such illers with silicas: U.S. Patents Nos. 2,470,577, 2,865,781, 3,152,001, 3,443,890 and British Patent No. 838j903. The other deals with in situ precipi-tation o~ insoluble silicates over the filler surace:
U.S. Paten~s Nos. 29259,481, 2,259,4829 292S9,483, and 4~167,423.

SUMMARY OF THE lNV~NllON
By the present invention, silane-unresponsive calcium carbonate is easily and e~onomically transformed into a silane-responsive filler by treatment with solu~le sodium silicate.

DESCRIPTION OF THE
PRFFERRED ~ODIMENTS
A compositional manifestation o the present inven~ion is a calcium carbonate filler which comprises a mixture of (I) particulate calcium carbonate, (II) sodium silicate9 and (III) a silane coupling agent having the ormula R(Rl)aSi(X~3_a wherein ~ which con-~ains a carbon at~m directl~ bonded to the silicon atom of ~he above formula represen~s a func~ionally substi-~u~ed organic radical or a straight-cha~n alkyl radi al of from 7 ~o 22 carbQn a~oms~ ~ represen~s a radical selected fr~m the group consisting of R and monovalant --2~

~ 3 ~3 126~5 hydrocarbon radicals containing from 1 to 6 car~on atoms, a ~as a value of 0 or 1~ and X represents a hydrolyzable group, the hydrolyæates of said silanes, the condensates of said ~ilanes, and mixtures thereof, which composi~ion has been heat:ed ~o a temperature in the range about lOO~C ~o about 140C for.a period of time in the range about one to about eight hours.
The organosilane coupling agents (III) and/or me~hods for their preparation are well known in the art and includè e.g. organofunctional silanes having the or~ula given above wherein R which contains a carbon atom dircctly bonded to the Si atom of the above formula represents a functionally substituted organic radical, Rl represents a radical selected ~rom the group consisting o R and monovalent hydrocarbon radi-cals containlng ~rom 1 to 6 carbon atoms 9 e.g. phenyl and alkyl radicalsg especially methylg a has a v~lue of 0 or 1, preferably 0, and X represents a hydrolyzable group the hydrolyæa~es of said silanes, the conden-sa~es o~ said silanes~ and mix~ures thereof. Illustra-ive of the more preferred functionally subs~ituted organic radicals are unsa~urat2d organic radicals such as olefinic radiczlsg e.g. vinyl, allyl, gamma-methacryloxypropyl ~ and l:he like; aminosubstituted radicals such ~s aminoalkyl radicals e . g . be~a-amino-~.~hyl, gamma-aminopropyl~N-beta~aminoethyl) gamma aminapropyl, a~d the like; epoxy su~stitu~ed radicals

-3-~9~3~3~

such as beta-(3,4-epoxycy~lohe~yl)-ethyl~ gamm~-glyci~ox~propyl, and the like; and mer~apto substituted radicals, such as beta-mercaptoethyl, gam~a-mercap~o-propyl~ and the like. Among ~he more preferred silane coupling agents that may be mentioned are vinyltrichlo-rosilane~ vinyl~riethoxysilane a vinyl~rimethoxysilane~
vin~ltris(2 methoxyethoxy)-silane, gamma-methac~ylG
propyltrimethoxysilane, beta-(3~4-epoxycyclohexyl)-ethyltrlmethoxysilane, gamma-glycidoxypropyl~rimethoxy-silane ~ vinyltriacPtoxysilane, beta~ mercaptoethyltrieth~
oxysilane~ gamma-mercaptopropyltrimethoxysilane, beta-aminoethyltri~thoxysilane, gæmma-aminopropyltriethoxy-~ilane~ gamma-aminopropyl~riethoxysilane, N-be~a-(aminoethyl)-gamma-aminopropyltrimethoxysi~ane, and the like.
~ dditional silanes which may be used ln ~he practice o this in~ention include the following:

~33~
HOOC(C~I2)8CHsi(OC~3)3 C~3CH2=CH(CH2)4CH2Si(OCH3)3 ttCH2CH2~--a ~C~2 =0 ~ ~ 2)3S ~ 2 3)3 ~CH2C~ ~CH~CH~]

~ Si(OCH3)3 HooCCH2CH25i(0CH2CH3)3 NCCH2CH2si~0~l2~ 3)3 2N(C~12~4Si~OC2Hs)3 H2NC~2CH2NHCH~CH2NHC~2C~2CH2Si( 2 5 3 ~2NC~HC~2CH2CH2si(oc~3)3 O C-NH

NcNHcH2cH2~(c~2)3si(OcH3~3 O H2N--C;O
H2NC-NH(CH2)N-(CE12)2-NH(CH~2)3Si(OCH3)3 polyethyleneimine-(CH~)3Si(OCH3)3 polyethyleneimine-C(CH2)3Si(OCH3)3]2 ~3NtCH2)3Si(oC2H5)3 CH2NHCH2CH~N(CH2)35i(0CH3)3 .

~C1 HOCH2CH2CH2Si(OC2H5)3 H2NCH2Si(OcH2~5)3 HOC~2Si~OCH3)3 H2NC~C~2si~ 5)3 polyazamide-rC~2CH2CH2Si(OCH3)3]1_5 ~see U.S. Pat. No. 3,746,348, patented July 17, 1973, for a complete description of silylated polyaæamides) CH2~C(CH3)COO(c~2)3si(O~ 2 2 3 3 6~4 '~
`~.,, 3~

CH2 =CHe~ 2M 2 2 2 2 2 ( 3 ) 3 o ~I H
CEI2 =CHC--NCH2CH2HN ( CH2 ) 3S i ( OCH3 ) 3 CEI2 C~ICN~I ( CH 2 ) 3 S i ( OC~l 2 CH 3 ) 3 CH2=CHCH2Si ( OCE12CE~20CH3 ) 3 CH2= 1C-CE~2si (OcH3 ) 3 HSCH2Si (oC~3 ) 3 HSCH2S i ( OCH2CH3 ) 3 HS- ~) -CE12CH2Si ( OC~12CE[3 ) 3 c~3 HS- ~ CH2CE12Si ( oCE12CEI3 ) 3 O O
NOCCHCCHC oCH2CH2CH2Si ( OCH3 ) 3 o HSCH2CE12CH2CNEI ( CH2 ) 3Si ( OCE~2CH3 ) 3 EIGcH2cH2cH2cEI2cH2cNEI ( CH2 ) 3Si (OCH2H5 ) 3 (CH CH~0)3SiC~2CH2CH2S-S-S-CH2CH2CE~25i( 2 3 3 ( CE13CH20 ) 3Si ~ CH 2 ) 3-S-S - ( CH2 ) 3S i ( OCH2CH3 ) 3 [ ( CH 3CH 2 ) 3S i CH 2CH2~3CH 3 ~ 2 L ~S -S ~S - ]
[(CH30)3SiC~IzCH2~ H3)2[S4]

CH2 ~ CHSi ( OCH3 ) 3 o CH3CE~20CE~H ( CH2 ~ 3Si ( OC2EIS ) 3 -Sa-~' ~3;~

HO ~ ~,~ C ~
~H3 I
Cfl2 C~2Si(OCH3)3 and other coupling agents known to those skill in the art such a6 octyltrimethoxysilane, monyltriethoxy-silane, dodecylmethyldichloro6ilane, and the like.

-5b .,,i ~, ~ ~ 9 ~ 126~5 As used herein, the terminology "coupling agent" refers ~o silanes contaLining one or more hydrolyzable groups which interact with calcium car-bona~e and one or more organic ~roups which react with or are compatible with polymeric substrates.
. Commercial soluble sodium silicates include sodium orthosilicate (Na4SiO4), sodium metasilicate (Na2SiO3), sodium disilicate (Na2Si~05~, and some more highly silic ous sodium silicates whose Na20:SiO2 ratios approach 1:4, a very common exæmple of which is called "water glass" (Na20:SiO2 in a 1:3.3 ratio).
Sodium metasilicate has ~een found to be a convenien~
soluble sodium silicate to use in the present inven-tion; others however would also be useful.
The amount o~ sodium silicate (II) to be us~d ac~ording to the present invention ranges from about 0.1 to about 10 percent based upon the weight o~ the calclum carbonate (I). The grea~er the Sllr-face area of the calcium carbonate, ~he more sodium ~ilicate re~uired. A preerred range is r~m ~bout 0.3 to about 3 percent, and more preferably to about 1 percent.
The amount of silane coupling agent (III) that can be employed in forming the silane-modified ~odium silicate~treated calcium carbonate compositions of this invention is not narrowly critical. It can ~6--126~5 conceptually rang~ from about 0.01 to about 50 percent based upon the weight of the calcium carbonate (1), but will more generally range from abou~ 0.1 to about 10 percent.
Processing parameters which may be ollowed according to the present invention are not narrowly critiral. Two approaches which ha~e been found ~o be ef~icacious are the "Wet Slurry Process" and the "Dry Blending Process".
In the Wet Slurry Process, calcium carbonate is mixed with two or three times its weight in water9 although more or less may be used. The sodium sili-cate ls mlxed into the calcium carbonate slurry, and, ~ubsequently, the silane is mixecl into the sodium silicate-treated slurl~, conveniently in the form of a premix with methanol or ethanol and water or aluminum nitrate, to enhance disper3ion. The silar nated slurry is then filtered, and the sollds are ovell-dried, e.g. at about 100C ~o about L40C or ~rom about 1 to about 8 hours. The dried solids may then be stored until used.
In the Dry Blanding Process, an aqueous solution of sodium silicate is blended with calci~m carbonate. To the blend is added the silane, con veniently mixed with a carrier such as microcrystal-line cellulose to facilitate handling. The silanated ~7--~3~ 68~

mixture may be ~u~bled, oven-dr:ied for a short period, and re-t~nbled hot3 to insure good ml~in~. Finally~
the ~ompositiorl is hea~ reated for from about I to about 8 hours a~ from about lOO~C to about 140C.
As indicat:ed above, by ~che present invention, s:ila~e-unresponsi~e calcium c~rbonate is easily and economically transfo~ed into a silane responsive filler by ~reatment with soluble sodilml silicate.
By contrast, prior art such as U. S . Patent No .

4,1673423 requires an in situ precipitation of insolu-ble silicate over the calcium carbonate surface.
Examples hereinbelow demonstrate by various means that, by the present invention, soluble sodium silicate can in fact be usPd to improve the bonding of silanes to calcium carbonate.
The organosilane-modiied sodium silicate-treated calcium carbonate compositions o the present invention can be used as reinforcin~ fillers in polymer composite formations in ~he manner described for organosilane-modified other metal silicate-~reated mineral composltions in U.S~ PateTIt No. 4,167,423.
~e improved ~ilane-calcium carbonate bonding achieved by the present invention would be expected ~o result in i~nproved bonding o the 17er ~n composite based on rubber9 polyesters3 ~nd the like. They may thus be ~ployed ~ rubbers, thermoplastic a~d thermosetting resins, paints ~ ~arnishes, inks ~ a~d the like .

~;

, ~ "

3~

EX~MPLES
The following Example.s serve to illustrate the present invention. Examples 1 and 2 demonstrate the preparation of sodium silicate-treated calcium carbonate fillers according to the present invention, while Ex~nples A ~nd B for comparison show similar calcium carbonate fillers which have not been treated wi~h sodium silicate and which are not wi~hin the scope of the present invention.

EXAMPLE A
To a m;xing bowl were added 400 grams of particulate calcium carbon.ate and 1200 grams of dlstilled water.
The calcium carbonate and water were mixed at 1500 revolutions-per minute for two minute~. Then, while m;~n~ con~i~ued, 8 grams of a premix consisting of 4 grams o~ octyl trimethoxysilane, 3.6 grams of methanol~ and 0.4 grams of distilled water were added.
After the addition was comRlete, m~X;ng was continued for 45 seconds. The mixture was then filtered, and ~he filtrate was dried for ~wo hours a~ 110C, where upon all large chunks were broken Up and drying was conti~ued ~or one hour at 1~0C.

EXAMP~E B

To a m;X;ng bowl were added 400 grams of particulate calcium carbonate and 1~00 græms o~ distilled wa~er.

_g_ The calcium carbonatP and water were mixed at 1500 revolutions-per-minute or two minutes. Then) while m;x;nE continued, 8 grams of a premix consisting o 4 grams of octyl ~rimethoxysilane, 3.6 grams of methanol, and 0~4 grams of aluminum nitrate were added.
A~ter the addition was complete~ m;~;ng was continued for 45 seco~ds. The mixture was then filtered, and the filtrate was dried for two hours a~ lOQC, where-upon the large chunks were broken up and drying was conti~ued for one hour at 110C.

EX~MPLE 1 To a m;x~ng bowl were added 400 grams of particulate calcium carbonate and 1200 grams of distilled water.
The calcium carbonate and water were mixed at 1500 revolutions-per-minute for two minutes. Then, the f~ller was treated with 4 grams of hydrated sodium me~asilicate. While m~lng continuecl, 8 grams of a premix con~lstlng o~ 4 grams o~ octyl trimethoxysilane~
3.6 grams of methanol, and 0.4 grams of distilled water were added. Ater the addi~ion was complete~
m~x~ng was con~inued for 45 seconds. The mixture was then filter~d, and the filtrate was dried for two hours at llO~C, whereupon the large chunks were broken up and drying was con~i~ued for one hour at 110C.

~ 12~5 To a m~ X;~ bowl were added 400 grams of particulate calci~m carbona~e and 1200 grams of distilled water.
The calcium carbonate and water were mixed at 1500 revolutions-per-minute for two minutes. Then, the fill~r was treated with 4 grams of hydrated sodium metasilicate. I~hile m;~;ng continuedg 8 grams of a premix consisting of 4 grams of oc~yl trimethoxysilane~
3.6 grams of methanol, and 0.4 grams of alumi~um nitrate were added~ A~ter the addition was complete, m~ng was con~inued for 45 seconds. The mixture was th~n fil~ered, and the filtrate was dried for two hours at 1104G, whereupon the large ch~mks were broken up and drying wa~ continued or one hour a~ 110C.

~2685 3~

CûNTACT ANG LES
. The followin~ table indicates the aging char-acteristics of the contact angle of silanated calcium carbonate samples obtained as in Examples A, B, 1, and 20 The contact angles were of distilled water drops on flat compressed pellets of the silanated caloium carbonate sample. The contact angles were measured as a function of the age of the drop on the pellet.

Contact Angles (in degrees) Tim~
~in seconds)Ex. A Ex. B Ex. 1 105 11~ - 14~
~0 96 109 150 148 ~5 105 150 148 ~80 ~3 91 150 148 240 90 ~5 150 14~

The samples corresponding to Ex~nples A and B, which contain no sodium silicate, show strong aging effects. The rapid decrease in contact angle is believed to be due to the c~mbine~ e~fect o a loss of silane from ~h~ surface and a lowering of the water's surface tensio~ by silane cont~min~tionG
In contrast~ the sæmples corresponding to Examples 1 and 2; which were treated with 50dium ~ ~.
L~-~ 3 ~ ~ 12685 silicateg show ~ery pronounced contact angles which do not a~e at all (at least within the four minute experi-mental time frame). This indicates a high degree of surface hydrophobicity and a s~able silane-filler bond. It is believed that the heat treatment of the s~mples promotes the formation of a strong chemical bond between the sodium silicate and the calcium car-bonate.

DRY BLENDI~G PROCESS
The following Examples demonstrate the dry (i.e., low level of wa~er) blending process which con-stitutes a prefexred process according to the present invention. Examples 3 and 4 illustrate the present invention; Example 4 has an additional early heat treat-ment as compared to E~ample 3. Examples C and D are presented for contrast and do not ~all within the scope of the claims, Example C corresponds to Example 3.
Example D shows the u~ of hydrophilic silica as opposed to the sodium silicate of the present invention.

EXA~SPLE 3 To a twinshell blender were added ~000 grams of calcium carbonate and 125 grams of a six percent by weight aqueous solution of sodium metasllicate. Blend-ing was carried out for one-half hour, at which point 20 grams of a dry silane concentrat~ (consisting of 70 ~ 12685 parts by weight of octyltrimethoxysilane dispersed onto 30 parts of rnicrocrystalli.ne cellulose for con-venience in handling~ was addecl and the mixture was tumbled for one-half hour. The mixture was .then oven-dried at 120~C for one-hal hour, subsequently tumbled for one half hour in hot condition, and finally heat-treated at 120C for two hours, after which it was stored.

EX~MPLE 4 To a twinshell blender were added 2000 grams of calclum carbonate and 125 grams of a six percent by weight aqueous 901ution o sodium metasilicate.
Blending was caxried out or one-hal~ hour, followed by a heat-treatment at 120C for two hours, at whLch point 20 grams o~ a dry silane concentrate (consisting o-f 70 par~s by weight o~ octyltrimethoxysilane dis-persed onto 30 parts of microcrystalline cellulose for convenience in handling) was added and thP mix~ure was tumbled ~or one~half hour. The mixture was then ove~-dried a~ 120~C o~ one-half hour, subsequently tumbled or one-half hour in hot conditiong and finally hea~-~reated at 120C or two hours9 ater which it was s~ored.

1~-33~n 1~6~5 EXAMPLE C
To a twinshell blender were added 2000 grams of calcium carbonate. Blending was carried out for one-half hour, at which point 20 grams of a dry silane concentrate (consisting of 70 parts by weight of octyltrimethoxysilane dispersed onto 30 parts of microc~ys~alline cellulose for convenience in handling) was added and the mixturP was tumbled or one-half hour. The mixture was then oven-dried at 1~0C for one~half hour, subsequen~ly ~umbled for one-hal~ hour ln ho~ condition, and finally heat-trea~ed at 120C for two hours, a~ter wh~ch it wa~ stored.

- EXAMPLE D
To a twinshell blendér were added 2000 grams of calcium carbonateO Blending was carried out for one-half hour and then 20 gram~ o a silica (Cab-o-Sil ~s 7S) were added and blendlng was con~inued for one-half hour, at which point 20 grams of a dry silane concentrate (consisting of 70 parts by weight of octyltrime~hoxysilane dispersed on~o 30 par~s of microcrystalllne celluLose for convenience in handling) was added and the-mixture wàs ~umbled for one-half hour. The mixture was ~hen oven-dried at 120C for one-half hour~ subsequently tumbled for one-h~lf hour in hot condition, and finally heat-~reated at 120C
for ~wo hours, after which it was s~ored~

3 ~

CONTACT ANGLES
The ~ollowing table indicates the aging characteristics of the contact angle of silanated calci~n carbonate samples obta-ined as in dry blend Examples 3, 4, C ~ and D . The contact angles were of distilled water drops on flat compressed pellets o~
the silanated calcium carbonate sample. The contact angles were measured as a function of the age of the drop on the pellet.

Contact Angles (in degrees) T~me (in seconds)Ex, 3 Ex. 4 Ex. C Ex. D

131 127 4~ ~1 120 ~31 127 34 32 ~10 131 ~27 1~ 11 The samples corresponding to Examples 3 and 4 show very pronounced contact angles which did not age at all with~n th exper~mental frame. This indi-ca~es a high degree of surface hydrophobiclty and stab~e silane-calcium carboIlate bonding~ .In con~rast~

s1m~larly produced samples C and D, which, howeYer, were ~ot treated wi~h ~;odi~n silicate according ~o ~he -~6 -3~

preserlt invention, sho~7 strong aging efects. The rapid decrease in contact angle is believed to be due to the com~ined effects of loss of sllanP from the calcium carbonate surface and lowering o the water's surface tensioll by silane contamination.

~ET SLURRY PROCESS

\

~3~

To a Denver cell mixer, available as the D-l type flotation machine from Denver Equipment Division, Joy Manufacturing Co., Colorado Springs, Colorado~ were added 400 grams of calcium carbona~e and 800 grams of water. Mixing was carried out for two minutes. Then 4.0 grams of sodium metasilicate monahydrate were added and mixing was continued for two minutes. To the resulting blend were added 8 grams of a premix composed of 4 grams of octyltri-methoxysilane, 3.6 grams of methanol, and 0.4 grams of 0.2N aluminum nitrate. Mixing was continued for two minutes, the mixture was filtered, and the solids were oven-dried at 120C for four hours.

EXAMPLE E
To a Denver cell mixer were added 400 grams of calcium carbonate and 800 grams of water. Mixing was carried out for two minutes and then 8 grams of a premix composed of 4 grams of octyltrimethoxysilane, 3.6 grams of methanol, and 0.4 grams of 0.2N alumlnum nitrate was added. Mixing was continued for two minutes, the mixture was filtered, and the solids were oven-dried at 120C for four hours.

~33~ 126~5 CONTACT ANGLES
Contact angles were determined as above with comparable results.

Contact Angles ~ ~in degre s) Time (in seconds) Ex. 5 Ex. E

9~ 140 ~
1~0 _ 45 2~0 14~ 90 36~ - 80 ~0 - 70 576 . ~40 60 go~ . - 4û

FILLER DESORPTION TEST
Another test which is lndicative of the degree to which ~he silane is bonded to the calci~m car~onate surace is the iller desorp~ion test (FDT).
In thi~ test a known æmount~ typically 0.1 gram, of treated sample is sprinkled on~o a pure water surfac~
possessing a 72.6 dy~es/cen~timeter initial surface tellsion value. The surface tenslon of the water i5 ~hen recorded as a unction of ~ime. If the silane is only physically adsorbed on ~he filler surface, ~hen it should slowly desorb and spread on the water~

3~ 12685 Such transfer of silane molecules should result in a change in surface tension of the water. On the con-tra~y, if the silane is chemically bonded to the filler ~urface and the bonds are stable even in the presence of water9 then one would not expect any change in wate~ surface tension with time. The treated particles in this case will remain hydrophobic and float on the water surface. Thus, the extent and the rate of change of surface tension of water as a function of time are a measure of the nature and the degree of silan2 bonding.

Surface Tension T~e ~in dynes/centimeter) (~n minutes) Ex. 3 Ex. 4 Ex. 5 Ex. C

3 63 ~ _ _ ~ ~ 54 72 33 7 - ~ 72 3 g _ _ _ _ ~ ~1.5 72 37 11 69 ~ - -12 _ 13 - 51.5 - 51.5 - 39 3~

The table depicts the FDT test results for ~arious silanated calcium carbonate surfaces. Here again, samples obtained using Treatment C~ containing ~o sodium silicate~ showed a rather rapid drop in surface tension indicating poor adhesion of silanc to the filler surface. Samples obtained through Treat-ments 5 and 3, both sodium silicate pre-treated and produced, respecti~ely, by the wet slurry and dry blend techniques, demonstra~ed excellent s~ability of silane at the surface, with the wet slurry treated one slightly outperforming the other. An interesting feature is the behavior of samples obtained using Treatment 4 which shows intenmediate stabîlity of the silane at the surface. Here, like the sample ~rom Treatment 3, the sample of CaCO3 was dry blended with sodi~ silicate solution. However, in this case, ~mlike the sample from Trea~men~ 3, the sample was dried at 1204C for two hours beore further reacting it with silane. The implication is that perhaps the loss of water has lowered the reactivity of ~hese sur faces towards siianes.
The overall implication of ~he above results îs tha~ ~he addition of sodium silica~e is cri~ical in developing a sil ne-responsive surface on caleium carbonate. The purpose of silîca~e addition i5 to ad~orb silica~e on the CaC03 ~hrough calcium silicate 3~3 bond formation leaving a large number of reactive silanol groups capable of reacting with added silane.
Mere addition of fine silica, which cannot chemically adsorb on CaC03, see Example D, does not yield the desired surface sensitization.
Various modifications and variations of this invention will be readily apparent to those skilled in the art. It is to be understood that such modifi-cations and variations are to be included within the purview of this invention and the spirit of the present claims.

. ;

Claims

WHAT IS CLAIMED IS:

1. A calcium carbonate filler composition which comprises a mixture of (I) particulate calcium carbonate, (II) sodium silicate, and (III) a silane having the formula R(R1)aSi(x)3-a wherein R which contains a carbon atom directly bonded to the silicon atom of the above formula represents an organic radical, R1 represents a radical selected from the group consisting of R
and monovalent hydrocarbon radicals, a has a value of 0 or 1, and X repre-sents a hydrolyzable group, the hydro-lyzates of said silanes, the conden-sates of said silanes, and mixtures thereof.
which composition has been heated to a temperature in the range 100°C to 140°C for a period of time in the range to one to eight hours.

2. A calcium carbonate filler composition as in Claim 1 wherein component (III) is octyl trimeth-oxysilane.