Surface modified pigments

This is application is a .Iadd.reissue of U.S. Pat. No. 3,290,165, Ser. No. 269,695 filed April 1, 1963, which is a .Iaddend.continuation-in-part of applicant's copending application Ser. No. 189,321, filed April 23, 1962, entitled "Surface Modified Pigments," and now abandoned.

This invention relates to finely divided particulate inorganic pigments modified with amino organosilanes and the process for their production.

When inorganic pigments are modified with the silanes according to this invention, the properties imparted to them are such that they can advantageously be used as fillers for thermosetting resins such as polyurethanes, epoxy polymers, melamine polymers, phenolic polymers, ureaformaldehyde polymers, unsaturated polyesters, as well as other polymers and elastomers including polyethylenes, polypropylenes, polystyrenes, saturated polyesters, polyamides, polyvinyl compounds, polyisoprenes, polybutadienes, polystyrenebutadienes, and the like.

The modified pigments can also be advantageously used as fillers for paper, paints, varnishes, inks, and paper coating compositions.

By the use of these modified finely divided particulate inorganic pigments, improved physical properties are imparted to the vehicles into which they are incorporated.

Inorganic pigments modified with amino organosilanes have affinity for direct dyes and are useful for imparting various colors to the vehicles.

An object of this invention is to provide modified pigments especially useful as fillers.

Another object of this invention is to provide modified pigments which are dyeable with direct dyes and are useful as color-imparting fillers.

A further object of this invention is to provide modified pigments which can be used as fillers in applications where they had heretofore been unsatisfactory.

A still further object of the invention is to provide cross-linkable fillers capable of imparting improved abrasion resistance among other improved properties to elastomers.

Other objects and advantages will be apparent from the following specification.

I am aware of extensive efforts in the prior art to improve properties of filler pigments by modification with organosilanes. Hydrocarbon silane modifications of pigments do impart improved dispersions in organic vehicles but such modifications do not normally increase reinforcement in vinyl addition polymers unless the hydrocarbon silane carries specific types of unsaturation which serves to promote a more tenacious bridge between the filler and the vehicle. In any case, all these prior art modified pigments are rendered hydrophobic by modification with either saturated or unsaturated hydrocarbon silanes and, furthermore, such silane modified pigments are not valuable reinforcing fillers in saturated thermosetting resins.

I have discovered that modification of filler pigments with saturated amino organosilanes improves reinforcement in a wide variety of vinyl addition as well as thermosetting polymers in that a strong chemical bridge between filler pigment and polymer results. Bridging is accomplished through the amino modified surface of the pigments. Surprisingly, amino organosilane modification improves reinforcement in both vinyl addition and thermosetting polymers, whereas unsaturated organosilane fillers are generally only effective in vinyl addition polymers where unsaturation is present. Another important advantage of amino organosilane modified fillers is that they are usually hydrophilic whereas prior art silane modified fillers are hydrophobic.

The modified pigments of this invention can be prepared by dissolving the desired amount of amino organosilane in a suitable solvent, adding the pigment and heating until the reaction is complete. The amount of modifier added depends upon the particular pigment being modified and the use for which it is intended. Generally up to about 15% by weight of the modifier is sufficient for most purposes.

A particularly useful process of modifying pigments according to this invention involves spray drying pigment slurries having one or more of the amino organosilanes dispersed therein. The spray drying process effects a uniform distribution of the modifier on the pigment and virtually instantaneously cures the modifier on the pigment.

The compounds used to modify the pigments can be depicted by the formula: ##STR1## wherein R 1 is hydrogen, alkyl, aryl, cycloalkyl, or alkylaryl; R 2 is hydrogen, alkyl, aryl, cycloalkyl or alkylaryl; R 3 is hydrogen, lower alkyl, aryl, lower alkylaryl, or loer arylalkyl; R 4 is hydrogen, lower alkyl, aryl, lower alkylaryl or lower arylalkyl; R 5 is hydrogen, lower alkyl, aryl, lower alkylaryl or lower arylalkyl; and X is alkylene, arylene, alkylarylene, arylalkylene, cycloalkylene having secondary and/or tertiary nitrogen present in the chain, and/or primary, secondary, and/or tertiary nitrogen pendant from the chain. Some of these amino organosilanes are disclosed along with methods for their preparation in U.S. Pat. Nos. 2,832,754; 2,930,809; 3,007,957; and 3,020,302. Commercially available amino organosilanes include "A-1100" (gamma aminopropyltriethoxysilane) and "Y-2967" (an amino silane which is a modified gamma aminopropyltriethoxysilane) sold by Union Carbide Corporation, N.Y., N.Y., and "Z-6020" (a diamino functional silane) sold by Dow Corning Corporation, Midland, Michigan.

.Iadd.Preferred compounds to modify the pigments are amino organosilanes of the formula:

H.sub.2 N--R--Si(OR').sub.3

wherein R is selected from the group consisting of phenylene, lower alkyl substituted phenylene, lower alkoxy substituted phenylene, and lower alkylene, R' is monovalent hydrocarbon group free of aliphatic unsaturation selected from the group consisting of lower alkyl, aryl, lower alkaryl and lower aralkyl, wherein R' can represent the same or different groups. .Iaddend.

Pigments advantageously modified in the practice of this invention are finely divided particulate inorganic pigments such as, for example, inorganic compounds of silicon, including hydrated or anhydrous silicas, calcium silicates, magnesium silicates, calcium-magnesium silicates, barium silicates, aluminum silicates, sodium-alumino-silicates, calcium-alumino-silicates, calcium-sodium alumino silicates; clays such as kaolins which include dickite, kaolinite and nacrite, halloysite, montmorillonites including sodium and magnesium bentonites, synthetic or natural zeolites; various metal oxides and carbonates such as zinc oxide, alumina, titania or magnesia, calcium carbonate; and various non-white pigments like carbon blacks, zinc sulfide, ferric oxide and the like.

All the above fillers are available on a commercial scale and include the following, all of which are finely divided, particulate substances.

Zeolex®, very finely divided precipitated sodium alumino silicate pigments of submicron particle size and disclosed in U.S. Pat. Nos. 2,739,073 and 2,848,346.

Zerosil®, very finely divided precipitated hydrated silicas of submicron particle size and disclosed in copending U.S. Pat. applications Ser. No. 144,168 filed Oct. 10, 1961, and 149,964 filed Nov. 3, 1961.

Suprex®, an air floated kaolin clay with platelike particles of which 87-92% are minus 2 microns.

Aromex®, intermediate super abrasion furnace carbon blacks.

Essex®, semi-reinforcing furnace blacks.

Silene EF®, a precipitated hydrated calcium silicate of very fine particle size.

Hi-Sil®, a precipitated hydrated silica of very fine particle size.

Celite®, a diatomaceous earth which is principally a hydrated silica.

Alumina C®, a hydrated aluminum oxide of small particle size.

Kadox®, a zinc oxide filler.

Titanox®, a pigment grade commercial titanium dioxide.

Cab-O-Sil®, a very finely divided anhydrous silica.

Ludox®, a precipitated silica of very fine particle size.

The following examples illustrate typical methods by which various pigments are surface modified in accordance with this invention.

Cured at

Unfilled

Filled

Modifier

Modifier

1% Z-6020

1% Z-6020

1% Y-2967

Physical Properties 305° F.

Control

Control

Water

Water

Water Benzene

Benzene

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200% Modulus 30 430 1,270

1,340

2,900

-- 2,900 1,710

60 500 1,310

1,530

2,990

2,890 1,710 --

75 510 1,330

1,480

2,820

-- 2,860 1,840

300% Modulus 30 830 1,570

2,070

3,190

-- 3,270 2,060

60 1,050

1,640

2,220

3,340

3,330 3,270 2,090

75 1,040

1,630

2,520

3,200

-- 3,240 2,170

Tensile Strength 30 5,240

4,340

3,680

3,770

2,960 3,470 4,040

60 4,890

3,850

3,920

3,490

3,620 3,290 3,610

75 5,320

3,640

3,560

3,510

-- 3,240 3,950

Elongation 30 500 570 470 425 190 365 560

60 440 525 450 335 360 315 500

75 450 505 440 370 -- 300 510

Hardness, Shore A 30 56 72 71 71 75 75 70

60 59 74 73 73 76 76 71

75 59 74 73 73 13 76 71

Crescent Tear 30 65 285 280 238 225 235 303

60 68 270 230 243 205 193 220

75 73 243 231 225 -- 193 225

NBS Abrasion Index, Percent

60 74.8 63.6 77.2 109.5

143.5 131.4 68.2

75 80.3 62.2 87.4 137.0

105.5 152.1 81.5

Hardness, Shore A, NBS Specimens

60 55 71 72 75 76 76 71

75 56 73 73 75 76 76 72

NBS Abrasion (Gum=100%)

60 100 85 103 147 192 176 91

75 107 83 117 183 141 204 109

Compression Set "B" 22 hrs./158° F.

60 5.5 34.0 17.5 11.3 10.1 12.0 25.0

75 5.1 36.7 16.5 12.0 9.5 11.0 23.9

Mooney Viscosity, ML 4'/212° F.

-- 44 60 65 65 83 65 64

Mooney Scorch, MS/265° F.

-- 23 26 20 16 12.5 18 23

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Table II demonstrates dramatic improvements in properties of polyurethane filled with amino organosilane modified clays.

When modified carbon black is used as the filler in a rubber recipe, good results compared to unmodified black are achieved with a 2% by weight modification using gamma aminopropyltriethoxysilane. The results listed in Table III are based upon tests in the following recipe.

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Parts/100 RHC

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Smoked sheet 100.0

ISAF carbon black

45.0

Zinc oxide 3.0

Stearic acid 3.0

Pine tar 3.0

Age rite HP.sup.1

1.0

NOBS special.sup.2

0.35

Sulfur 2.75

Total 158.10

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.sup.1 An antioxidant containing phenylbeta-naphthylamine and

N,Ndiphenyl-para-phenylenediamine.

.sup.2 Accelerator containing Noxydiethylene benzothlazol2-sulfenamide.

The batches were mixed on a Banbury using speed #1, ram pressure of 30 p.s.i., and a starting temperature of 125° F.; the final batch mix was on a 6-inch by 12-inch mill and the inlet water temperature was 158° F. The compound was cured for 70 minutes at 275° F., then tested. The results are listed in Table III.

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Abrasion,

Percent Modulus, Tensile,

Huber-

Pigment Modifier p.s.i. p.s.i. Williams

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ISAF Carbon Black

None 1,780 4,590 100.0

Control.

ISAF Carbon Black

.sup.1 1,970 4,720 107.9

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.sup.1 2.0% gamma aminopropyltriethoxysilane.

This data indicates that when carbon black is modified with controlled amounts of modifier, the properties which it imparts to rubber are improved in respect to modulus, tensile, and abrasion resistance.

When modified Zeolex is used as a filler for rubber compounds, it imparts to the rubber improved properties of modulus, tensile strength, tear resistance and abrasion resistance when compared to these same properties in rubber filled with unmodified Zeolex. The results in Table IV are based upon the following recipe:

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Parts/100 RHC

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GRS 1502.sup.1 100.0

Pliolite S6B.sup.2

20.0

Zinc oxide 3.0

Stearic acid 2.0

Cumar MH 21/2.sup.3

7.5

Zeolex 23 66.5

Santocure.sup.4

2.0

DOTG.sup.5 1.0

Sulfur 2.5

Total 204.5

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.sup.1 Emulsion copolymer of 23.5% styrene and 76.5% butadiene.

.sup.2 A styrenebutadiene copolymer of high styrene content.

.sup.3 Paracumarene-indene resin.

.sup.4 nCyclohexyl-2-benzothiazole sulfenamide accelerator.

.sup.5 Diortho-tolylguanidine.

The recipe was mixed on a Banbury mixer at speed #1, ram pressure of 30 p.s.i., and at a starting temperature of 125° F. The final batch was mixed on a 6-inch by 12-inch mill with a water inlet temperature of 158° F. The compound was cured at 292° F., then tested. The results are shown in Table IV.

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Cure 200% 300% 400%

Minutes Modulus Modulus Modulus

Tensile

Elongation

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PIGMENT-ZEOLEX 23 UNMODIFIED-CONTROL

5 80 -- -- 80 280

10 80 -- -- 80 280

15 470 650 860 1,300 605

20 720 1,000 1,350 1,640 460

30 750 1,060 1,450 1,560 420

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PIGMENT-ZEOLEX 23 MODIFIED WITH 10% GAMMA

5 690 1,010 1,340 1,970 580

10 910 1,300 1,710 2,480 550

15 1,010 1,400 1,820 2,360 510

20 1,070 1,480 1,920 2,280 470

30 1,090 1,480 1,940 2,360 480

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Abrasion Index.sup.1

Shore Hardness

Pigment 10' 15' 20' 10' 15' 20'

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Zeolex 23 Control

.sup.2 41.5 47.5 60 72 77

Modified Zeolex 23

61.7 63.0 62.3 76 76 77

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Tear Resistance, Avg.

Pigment 5' 10' 15' 20'

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Zeolex 23 Control

37.5 38.5 174 160

Modified Zeolex 23

216.5 193.5 195 187.5

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.sup.1 Percent of NBS Standard sample.

.sup.2 Not cured.

The results indicate that Zeolex 23 modified with gamma aminopropyltriethoxysilane, when compared with unmodified Zeolex 23 used as a filler for rubber, is faster curing, has increased modulus, increased tensile strength, and improved tear resistance and abrasion resistance.

It should also be noted that physical and "wet" electrical properties of filled resin systems can be significantly improved by treating the fillers in accordance with this invention.

I have found that in addition to the concepts disclosed above, the properties of the modified pigments are affected by the solvent used in their preparation.

The properties of carbon blacks, clays and silicates modified in aqueous systems, such as disclosed in Example 2, vary markedly from the properties of these same pigments modified in nonaqueous systems as disclosed in Examples 1 and 3.

In order to demonstrate these differences, regular Suprex clay, Suprex clay of Example 2, and Suprex clay modified in nonaqueous solvent according to the teachings of Example 7 were used in producing rubber compounds using the following recipe.

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Parts by weight

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Smoked sheet.sup.1 100

Clay (as specified in Table V)

104

Zinc oxide 5

Sulfur 3

Captax 1

Stearic acid 4

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.sup.1 Natural rubber.

The compounds were mixed on a 6-inch by 12-inch laboratory mill and then cured at 260° F. to produce 30-, 45-, and 60-minute cures of each.

Table V below compares the abrasion index and the 200% modulus level of each of the test materials.

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Abrasion Index,

200% Modulus

Percent p.s.i.

Clay 30' 45' 60' 30' 45' 60'

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Suprex Control 55.0 55.9 53.7 760 960 990

Suprex 3% Modifier

72.8 68.6 65.2 2,000

2,070

2,170

(Benzene)

Suprex 3% Modifier

84.6 85.5 70.7 1,740

1,970

1,990

(Water)

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The results as set forth in Table V clearly indicate that clays modified in accordance with the invention impart superior properties to rubber compounds when used as a filler therein. These results also demonstrate that the clays modified in an aqueous system give a higher abrasion resistance and a lower modulus than clays modified in a nonaqueous system.

While natural rubber was used in the recipes tested in Table V, these tests were also conducted with similar results from recipes using SBR, polyurethanes and polybutadiene.

The foregoing is illustrative only and additional modifications may be made without departing from the substance of the invention as defined in the appended claims.