CA2023526A1

CA2023526A1 - Electrically conductive mixed-phase rutile pigment, process of producing the same and use thereof

Info

Publication number: CA2023526A1
Application number: CA002023526A
Authority: CA
Inventors: Clemens Aderhold; Wolf-Dieter Griebler; Jorg Hocken; Uwe Rosin; Gunther Rudolph; Takao Hayashi; Norihiro Sato; Manabu Hosoi; Nobuyoshi Kasahara
Original assignee: Individual
Current assignee: GEA Group AG; Mitsui Mining and Smelting Co Ltd
Priority date: 1989-09-01
Filing date: 1990-08-17
Publication date: 1991-03-02
Also published as: JPH03192160A; EP0415478A2; JP2884260B2; EP0415478A3; EP0415478B1; DE59004203D1; DE3929057A1

Abstract

ABSTRACT OF THE DISCLOSURE:
The invention relates to an electrically conduc-tive, inorganic color pigment, which consists of a mixed phase rutile pigment as a substrate, which is provided with an electrically conductive coating of tin oxide doped with antimony. The substrate has a BET surface area of 1 to 10 m2/g and the coating layer has a thickness of 2 to 80 nm.

Description

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This invention relate~ to an electrically conductive mixed-phase rutile pigment, to a process of producing the same and to the use of the pigment as an additive in the production of dyed anti~tatic plastics and dyed antistatic paints.
~ he electrically insulating properties of plastics are known. But plastics are increasingly required to have a certain electrical conductivity for special applications. In addition to the shielding of electronic components from external electromagnetic fields, (e.g., in the case of computer housings), ~uch applications particularly concern ca~es in which static electricity i~ to be discharged, e.g., in the packaging indu~try, for instance in the storage of explosives. Integr~ted circuit components etc., medical rubber article~, having an antistatic fini~h, wall-to-wall carpet~ having electro-static propertie~, anti~tatic "clean rooms~, electrically conductive metal-joining adhesives. Plastic components nhich are electrically conductive or provided with an electrically conductive surface ~ilm may be pro~ided with an electro-static paint.

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_ 2 -It is knoml to render polymer~ electrically conductive by an addition of conductive particles. For instanee, metal or carbon black particle3g semiconducting oxids~, such as zinc oxide, or iodides, ~uch a~ copper iodide, may be u~ed. A~ a rule, the polymer~ co~taining a commercially available additive ais a filler have a black color because they contain carbon black or metal particle~ although a black color i~ not de~ired in many ca~e~ Polymer3 containing, e.g., zinc oxide as a filler are not ~table as regard~ their electrical conductivity, and polymer~ containing, e.g., copper iodide as a filler are not 3ufficiently inert. Tin oxide doped with antimony may be unacceptable toxicologically. From European Patent Specification 025 583 it ii3 known to provide titanium oxide particle~ with a layer consi~ting of antimony-doped tin oxides ~he previou~ly known electrically conductive white powder may be tran~formed to an electrically conductive color pi g ent by an addition of dyestuffs or pigments.
Mixed-phase pigments having a rutile structure hav~ been known ~or a long time. Mixed oxides ~hich have a rutile structure a~d have hue~ eztending over ~ide regions o~ the visibl~ spectrum can be produced by an incorporation of metal oxide~, ~uch a~ NiO, Cr203, CuO, MnO, together with Sb205, Nb205, W03 into the cry~tal .

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lattice of the titanium dioxide~ The mixed-pha~e rutile pigments which contain nickel and chromium have achieved a considerable commercial 3ignificance. I~ nickel oxide and chromium oxide as color-imparting oxides are incor-porated in ~iO2, metal oxide~ having a higher valency, particularly oxides o~ antimony but al~o of niobium and/or ~ung~ten9 are incorporated for a valency corn~en-sation. Such pigments are produced in that anata3 and/or hydrats~ of titanium dioxide together with incorporable metal oxide~ or precur~or compound~ thereof are ignited at temperatures of about 900 to about 1200 ~ and are ~ub~equently ground (~llmanns Encyclopadie der techni-~chen Chemie, 4th edition, volume 18 (1979), page~ 608-609)~
~he mixed-phase rutile pigment~ have a high re~istance to light, weathering, acid~ and alkalie~ and other chemical~
and are ~table at temperatures up to about 1000C. Owing to their excellent hue ~tability - resistance to light and weathering even under ~trong illumination in paints based, e.g., on alkyd-melamine resin~ or ~ilicone polye~ters and exposed to weathering, ~aid pigment~ are eminently ~uitable ~or pigmenting baked paints or paint~ applied by coil coating. But even the pigmenting of pla~tic~ with mixed-pha~e rutile pigment~ i~ increa~ing in importance. Mixed-pha e rutile pigment~ which contain chromium(III) oxide and which contain particularly antimony oxide but al~o ~, . . . .

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niobium oxide and/or tungsten oxide a~ metal oxide~ having a higher vPlency have achieved the highe~t economic ~ignifi-cance thus far.
It is an object of the invention to provids an electric~lly conductive color pigment which combines a ~table electrical conductivity and a high dieper3ibility in polymer~ and resins and ha~ a high hue stability in a wide range of hue~.
That object i~ accompli~hed by the invention by the use of an inorganic color pigment. In accordance therewith the invention is characterized in that the color pigment consists of a mixed-phase rutile pigment as a substrata, which is provided with an electrically conductive coating o~ tin oxide that i9 doped with antimony.
The coating produces variou~ desirable result3.
Wherea~ the pigment contain~, e.g., only 30~ by weight tin oxide, the entire product ha~ the ~ame electrical properties as pure, electrically conductive tin o~ide. In that connection, reference is made to the graph shown in Figure 1. ~he graph illu~trates the dependence o~ the electrical conductivity of a mixed-pha~e rutile powder that i~ coated with Sb-doped tin o~ide on the co~tent of ti~ dioxide (% by weight~O Becau~e the semiconductor layer is relatively thin, the color of the mixsd-pha~e rutile pigments i~ 3ubstantially preserved a~d the bright-ness is virtually not decreased (see Table 1). Becau~e the .

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electrically conductive pigments o~ the invention do not only render a polymer conductive but also impart a color thereto, the pigment volume concentration o~ 3aid pigment~
can be increa~ed to increase the final conductivity of a sy~tem without a need for additional (non-conductive) color pigments. This con~titute~ an advantage over co~mercially available bright pigments which have no color.
A requirement for a wide use of such pigments is an adequate bond str~ngth of the doped tin oxide layer on the substrate consisting of the mixed-pha~e rutile pigment even during a typical processing (grinding, dispersing, etc.). A high adhe~ion of the applied layers to mixed-phase rutile color pigments i~ ensured by crystal chemistry. As the crystal structure o~ the mixed-phase rutile color pigments correspond~ to the cry~tal struct~re of the tetragonally crystalliæing tin dioxide layer, an epitaxial growth is permitted.
~ he amount in which the electrically conductive tin oxide (doped with antimony oxide) .i3 required for an adequate electrical conductivity will depend on the surface area of the mixed-pha~e rutile pigment ~hich i~ employed. It mu~t be po~ible to form on the substrate a coherent semiconductor layer in a sufficient thickne~s. A thic~ness below 2 nm o~ ths layer will not be sufficient and a thickness above 80 nm will increase the risk of a detaching ~, " , , ,: . . ~ ,. ~
. ,, ' ' 2~23 ~ 6 of the ~emiconductor layer a~ the pigment i~ incorporated in a system. In the range above 80 nm the electrical conductiv-ity approaches a limit. Whereas the dark blue to black color of the pure semiconductor predominates increa~ingly~ the advantage afforded by the pre3ent invention and residing in the provi~ion of conductive mixed-pha~e rutile color pigment~ will be lo~t. For this reason the layer has prefsrably a thickness between 10 and 30 nm.
If the mixed-pha~e rutile pigment has a t~pical BET surface area o~ 1 to 10 m2/g, preferabl~ of 3 to 5 m2/g, the proportion of the ~emiconductor layer will amount to about 30~ by weight.
Besides, the conductivity which can be achieved in a mixed-phase rutile color pigment which in accordance with the invention is provided with an electrically conductive coating will depend on the antimony content (calculated as Sb oxide) o~ the tin dioxide 1ayer. ~he antimony co~tent generally amounts to 1 to 15 ~ by weight Sb oxide, particularly to 2 to 12 ~ b~ ~eight (related to 6 to 12 tin dioxide). In that range, an adequate electrical conductivity is combined with only small lo~es of the optical propertie~ of the mixed-phase rutile color pigment~, ~uch as hue stability.

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The mixed-phase rutile color pigments of the invention have a~ electrical conductivity be~ween 1.2 x 10 4 and 7 x 10 2 (ohm-cm) 1. ~he electrical conductivity of powders con~i~ting of electrically co~ductive mixed-phase rutile pigments is determined by a measurement of the volume resistance o~ small plates having a thicknes~ of 1 to 5 mm.
For that purpo~e the powders are compacted under a pre~sure o~ 90 bars to form ~mall plates and -the resistance i8 mea~ured with electrodes applied under a pres~ure of 2 to 5 bars.
The invention relates also to a process of producing the electrically conductive mixed-phase rutile color pigments. In the process, an aqueous di3persion of a mixed-phase rutile pigment in a mineral acid is mixed with a solution of hydrolyzable tin compounds in a mineral acid and with a solution of hydrolyzable a~timony compounds in a mineral acid, the pH value i~ increa~ed to effect a hydroly~is o~ the hydrolyzable compound~, and ~he mixed-phase rutile pigment which has been coated ~ith the precipitated hydroxides i9 optionally aged and i9 separated, dried and calcined.
~ he mineral acid ~olution~ which contain the hydrolyzable compounds of tin and antimony may be added to the aqueious disper~ion of the mixed-phase rutile pigment in a miner~l acid at the ~ame time 80 -that the compounds will be hydrolyzed at the same time in the presence of the mixed-phase rutile pigment as the p~ value is increased. It . - .. . . . .

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will be more de~irable, however, to add the mineral acid solution~ of hydrolyzable compound~ to the aqueoua di~per-~ion of the mixed-pha~e rutile pigment in succesYion and each of them i~ added after the tin compound has been hydrolyzedO
The di~persion and the mineral acid ~olutions are suitably rendered highly acidic (pH 0 to 2) with hydrochloric acid although ~ulfuric acid may be used too.
The hydrolyzable compound~ employed suitably consist of the halides of tin and antimony, preferably of their chlorides, such a~ tin tetrachloride and antimony trichloride.
In carrying out the proce~ according to the invention a su~pensîon o~ a mixed-pha~e rutile pigment in water i9 prepared fir~t and the su~pen~ion is a~justed to a highly acidic pH value ~0 to ~), prefsrably ~ith hydrochloric acid. The solid~ concentration is limited only by the requirement for a uniform, homogeneou~ 9U~-pen~ion and generally amoU~tB to 10 to 500 ~ 1. By mean~
of a hydrolyzable ti~ compound~ pre~erably tin tetra_ chloride, in a ~mall amou~t of abou~ 1 to 5 ~ of the total amount required, the sur~aces o~ the mixed-pha~e rutile pigment are prepared for the ~ubsequent coating step. ~fter an adjustment to a pH value in exce~ o~ 10 2 0 2 ~ ~ 2 ~

with a strong ba~e, preferably sodium hydroxide solution, additional base and additional hydrolyzable tin compound9 which is contained in a mineral acid, preferably a solution of SnC14 in HCl, are added at the same time while a constant pH value is maintained~ The addition i8 preferably effected at an elevated temperature in the range from 60 to 80 C. To complete or impro~e the SnO2aq layer the pH value is then decreased into the acid range, preferably to O to 2, with hydrochloric acid~ The doping component consisting of a hydrolyzable antimony compound, preferably SbC13, is then added preferably at an elevated temperature~ Thi~ may be succeeded by an aging of the hydroxide gel~ in order to form a semiconductor precur~or. Such aging will re~ult in a more homogeneous distribution of the antimony hydroxide in the matrix of tin hydroxide, i.e., in improved semicon- ~:
ductor properties.
If the concentrations of tin and antimony are calculated from the solubility products ~p Sn(OH)4 : 56;
K8p Sb(OH)3 : 41.4) and are plotted again~t the pH value~ ~:
two straight lines will be obtained, which have different 810pc9 and intersect at about pH = O. Beca~se tin and antimony ha~e about the same ~olubility adjacent to the point of intersection, a ~ufficient number of cycle~ in which the hydroxide lattice is built up and disintegrated - , - , ; ;,- , .

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in the micro~copic range during the agi~ will result in a uniform distribution of tin and antimony.
The conçentrations of the hydrolyzable tin and antimony compound~ will depend on the phy~i¢al properties of the compounds which are employed and lie between 0~1 and 500 g/l. It is merel~ neces~ary that the solution~
which are added do not contain hydrolyzable compound~
which have a lower solubility than the hydroxide~ and oxides of ~aid element~ under the prevailing conditions.
After a solid-liquid ~eparation, the coated mixed-phase rutile pigment is dried and is rendered electrically conductive by being ignited at a temperature of 300 to 800 C, preferably 400 to 600 C~
The mixed-phase rutile pigments produced by the procesY in accordance with the invention are electrically conductive and have a color depending on the composition of the substrate. Said pigments have a stable electrical conductivity, a high dispersibility and a high hue ~tability and are particularly ~uitable for being incorporated in and for dyeing plastic~ and paints and for imparting aati~tatic properties thereto~ For thi~ rea~on a further subaect matter of the invention i8 th~ u~e of the ~lectric~lly conductive mixed-phase rutile pigments for dyeing and ~or imparting antistatic propertie~ to pla~tics, synthetic ~ibers, and laminated paper~, for producing electrically conductive adhesive jointY or for producing dyed paints having anti~tatic properties.

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, The invention afford~ advantage~ Electrically conductive mixed-phase rutile color pigment~ are provided as well ag a proces~ by which they can be produced in a simple manner. ~he product~ have a stable electrical conductivity and can homogeneou~ly be disper~ed in pla~tics and ~ynthetic fiber~ and can be used to impart color virtually without a need for additional color pigment~
and to impart antistatic properties to the products.
~he ~ame remarks are applicable to paints, coating com-positions and adhe3ive compositions which contain the electrically conductive mixed-phase ru~ile pigm~nt~ of the invention.
~ he invention will be explained more in detail and by way of example with reference to the following Example~.
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100 g of a mixed-phase rutile pigment which contained (Ti, Ni, Sb) oxide (Sicotan Gelb ~ 1010 of BASF AG) (surface area 3 m2/g) were 3uspended in 400 ml water of 70C and were adjusted to pH 2 with hydrochloric acid. 500 ml water at 70C ? 1 ml SnC14 and 1 ml ~Cl (concentrated) were then added. The resulting yellow suspension was ~ub~equently stirred at pH 1.5 for 60 min-utes. 800 ml 101o NaOH and 31 ml SnC14 dis~ol~ed in 100 ml 2 ~ HCl were added at the same time~ ~ollowed by stirring . . , , , . , ., , . , . : . , .

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~or 30 minutes. The total duration of that ~tep amounted to 120 minute~ and the temperature ~Na~ 70C. The pH value was ~educed to 2.5 with HCl and 5.3 g SbCl3 di~solved in 100 ml 2 M HCl and 170 ml 101o NaOH ~ere added in drops at the same time during the next 90 minutes. The yellow suspension was kept at 70C for 20 hours. ~he ~olids were subsequently separated and dried. ~fter an ignition at 500C (1) and 600C (2) the powder had a conductivity of ~1) 1.4 x 10 4 (ohm-cm) 1 and of (2) 5~1 x 10 3 (ohm-cm) 100 g of a mixed~phase rutile pigment containing (~i, Cr, Sb) oxide (d50: 1.3 ~ )(1) (Ferro P 630 of Ferro~
were ~uspended in 400 ml H20 and adiu~ted to pH 2 with hydrochloric acid. 500 g H20, 1 ml SnCl4 and 1 ml con-centrated HCl were the~ added ~o that a p~ value of 1.5 was obtained. The orange-colored suspension ~as stirred at room temperature for 1 hourO 500 ml 10~ NaOH were then added and the ~uspension was heated to 70C. A ~olutio~ of 31 ml SnC14 in 69 ml 2 ~ HCl was added in drops within 90 minutesO Additional 20 ml 1~ NaOH had to be added to stabilize the pH ~alue. ~he orange-colored ~uspension ~ .
(1) "d50 in ~ is the median ~alue of the particle size distribution. It is the geometric median of all particle diameters, i.e., the particle size that iq a~sociated with a "residue~ o~ 50%.

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_ 13 -was stirred at 70C for 0.5 hour. Thereafter, about 110 ml 2 ~ HCl were added in drops within 1,5 hours 90 that a pH value of Z.5 was obtained. 120 ml 10~0 NaOH
and 100 ml of a ~olution of 5.3 g SbCl3 in 100 ml 2 M HCl were then added in drops at the ~ame time and some drop~
of concentrated HCl were added ~o maintain a con~tant pH
value~
The orange-colored suspension was then stirred at 70C for 20 hours. After 20 h the suspen~ion was filtered and washed. The product was dried at 110C and was sub~e-quently ignited at 600C for 1 hour.
The powder had a conductivity o~ 2.7 x 10 2 (ohm-cm) 1.
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100 g of a mixed-phase rutile pigment containing (~i, Ni, Sb~ oxide (Ferro P 610 of Ferro~ d50 = 0-9 ~m) were suspended in 400 ml ~ater and were acidified to pH 2 with HCl. 500 g H20, about 2 ml concentrated HCl and 1 ml SnC14 were then added 50 that a pH value of about 1.5 was obtained~ ~he yellow su~pension wa~ ~ubsequently ~tirred at room temperature for 1 hour. 500 ml 10% NaO~ were then added. ~he suspension wa~ heated to 70C. A ~olution of 31 ml SnC14 in 69 ml 2 M HCl wa~ ~hen added in drop~
within 1.5 hours. Because the pH value should not decrease below 11.5 during the addition in drops, additional . .
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140 ml 10% NaOH were added. The yello~ su~pen~ion wa~
~ubsequently stirred at 70C for 0.5 hour~ Thereafter, about 210 ml 2 ~ HCl were added in drops within 1.5 hours 30 that a pH value of 2.5 was obtained. 115 ml 10~0 NaOH
and 100 ml of a solution of 5 3 ml SbC13 in 100 ml 2 M HCl were ~ubsequently added in dropY at the ~ame time as well as some drops of concentrated H~l 90 that the pH value of the suspe-n~ion remained constant~
The product wa~ then ~tirred at 70C for 20 houxs.
The product w~;ch had been filtered of~ and had been dried at 110C was then ignited at 600C for 1 hour.
The powder had a conductivity of 6.5 x 10 2 (ohm-cm) 1.

100 g of a mixed-pha~e rutile pigment containing (Ti, Cr, Sb) oxide (Sicotan ~ 2010 of BASF ~G~ ~urface area 5 m2/g) were ~uspended in 400 ml water and acidified to pH 2 wqth HCl 500 g ~2' about 1.5 ml concentrated HCl and 1 ml SnC14 were then added 50 that a p~ value of about 1.5 was obtained. The orange-colored su~pension wa~
stirred at room temperature for 1 hourO 500 ml 10% NaO~
were then added and the ~uspe~ion wa~ heated to 70C~
Thereafter, a solution of 31 ml SnC14 i~ 69 ml 2 M HCl was added in drops within 1.5 hour~ Because the pH value ~hould not decrea~e below 11.5 during the addition in drops, `: ..
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additional 85 ml 10~ NaOH were added. ~he orange-colored suspen~ion was stirred at 70C for 0.5 hour. About 210 ml 2 ~ HC1 were then added in drop~ within 1.5 hour~ so that a pH value of 2.5 was obtained~ 115 ml 10~ NaOH and about 100 ml of a ~olution of 5~3 g SbC13 in 100 ml 2 ~ HCl were added in drops at the same time as well as some drops of concentrated HCl 90 that a pH value of about 2.5 was obtained. The addition in drops wa~ terminated after 1 hour. The produc~ was subsequently stirred at 70 for 20 hour3. The orange-colored product which had been filtered off was ~ubsequently dried at 110C and was ignited at 600C for 1 hour.
~ he powder had a conductivity of 4.9 x 10 2 (ohm-cm)~1.
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100 g of a mixed-phase rutile pigment containing (Ti, Ni, Sb) o~ide (Sicotan L 1012 of BASF AG, surface area 3 m2/g) were ~uspended in 300 ml water and adjusted to pH 2 with H~l. 600 ~ H20 and about 1 ml concentrated HCl were then added ~o that a pH value of about 105 was obtained.
~he yellow suspension wa~ subsequently stirred at room temperature for 1 hour. 500 ml 10~ NaOH were then added and the su~pension was heated to 70C. A solution of 31 ml SnCl4 in 69 ml 2 M HCl was then added within 1.5 hours. Additional 120 ml 10~ NaO~ were added becau~e .. . . .; . : , . .
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_ 16 _ the pH value should not decrea~e below 11.5 during the addition in drops~ The yello~ ~u8pen~ion was subsequently 3tirred at 70C for 0.5 hour. ~hereafter, abo~ 120 ml 2 M ~Cl were added in drop~ within 1.5 hours ~o that a pH value of 2.5 wa~ obtained. 115 ml 10~ NaOH and 100 ml of a ~olution of 5.3 g SbCl3 in 100 ml 2 ~ HCl were then added in drops as ~well as some drope of concentrated HCl so that the pH value amounted to about 2.5. The addition in drop~ was terminated after 1 hour. Thereafter, the yellow suspension wa~ stirred at 70C for 20 hours and wa~ filtered. The resulting product wa~ dried at 110C
and wa~ sub~equently ignited at 600C for one hour.
The powder had a conductivity of 1.1 x 10 2 (ohm-cm) 1.

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Table 1 Brightnesse~ of Mixed-pha~e Rutile Color Pigment~
Type of Pigment Brightnes~ reference Decrease of ~ brightne~s _ __~ __ __ __ ___, Untreated (Ti, Ni, Sb) Oxide Sicotan L 1010, BASF AG 82~2 59.8 15.1 (Ti, Cr, Sb) oxide Ferro P 630 47.2 43.8 7.2 (Ti, Ni, Sb) oxide Ferro P 610 80.6 53. 319,0 (~ri, Cr, Sb) oxide Sicotan L 2010, BASF AG 54.5 45.0 17.4 (~i, Ni, Sb) oxide Sicotan L 1012, BASF AG 85.1 72.7 14.6 :~ , . . .

Claims

1. An electrically conductive, inorganic color pigment, characterized in that the color pigment consists of a mixed-phase rutile pigment as a substrate, which is provided with an electrically conductive coating of tin oxide that is doped with antimony.

2. An electrically conductive inorganic color pigment according to claim 1, characterized in that the substrate has a BET surface area of 1 to 10 m2g.

3. An electrically conductive inorganic color pigment according to claim 2, characterized in that the substrate has a surface area of 3 to 5 m2/g.

4. An electrically conductive inorganic color pigment according to claim 1, characterized in that the substrate has the same crystal structure as a coating layer of Sb-doped tin dioxide (cassiterite).

5. An electrically conductive inorganic color pigment according to claim 1, characterized in that the coating layer has a thickness of 2 to 80 nm.

6. An electrically conductive inorganic color pigment according to claim 5, characterized in that the coating layer has a thickness of 10 to 30 nm.

7. An electrically conductive inorganic color pigment according to claim 1, 2, 3, 4, 5 or 6, characterized in that the coating layer of tin dioxide contains 1 to 15%

by weight antimony oxide.

8. An electrically conductive inorganic color pigment according to claim 1, 2, 3, 4, 5 or 6, characterized in that the coating layer of tin dioxide contains 6 to 12%
by weight antimony oxide.

9. A process of producing an electrically conductive inorganic color pigment, characterized in that an aqueous dispersion of a mixed-phase rutile pigment in a mineral acid is mixed with a solution of hydrolyzable tin compounds in a mineral acid and with a solution of hydrolyzable antimony compounds in a mineral acid, the pH
value is increased to effect a hydrolysis of the hydrolyzable compounds, and the mixed-phase rutile pigment which has been coated with the precipitated hydroxides is optionally aged and is separated, dried and calcined.

10. A process according to claim 9, characterized in that the mineral acid solutions which contain the hydrolyzable compounds are added to the aqueous suspension of the mixed-phase rutile pigment in succession and each of them is added after the tin compound has been hydrolyzed.

11. A process according to claim 9, characterized in that the solutions which contain hydrolyzable compounds are hydrochloric acid solutions.

12. A process according to claim 9, characterized in that the hydrolyzable compounds are tin(IV) chloride and antimony(III) chloride.

13. A process according to claim 9, characterized in that part of the mineral acid solution of the hydrolyzable tin compound is initially added to the aqueous dispersion of the mixed-phase rutile pigment at a pH value below 3 and the main amount is subsequently added and is hydrolyzed at a pH value above 10, whereafter the mineral acid solution of the antimony compound is added and is hydrolyzed at a pH value below 3.

14. An electrically conductive mixed-phase rutile pigment according to claim 1, 2, 3, 4, 5 or 6, for dyeing and for imparting antistatic properties to plastics, synthetic fibers, laminated fibers, for producing electrically conductive adhesive compositions or for producing dyed paints having antistatic properties.

15. A process according to claim 10, characterized in that the solutions which contain hydrolyzable compounds are hydrochloric acid solutions.

16. A process according to claim 15, characterized in that the hydrolyzable compounds are tin(IV) chloride and antimony(III) chloride.

17. A process according to claim 10, 15 or 16, characterized in that part of the mineral acid solution of the hydrolyzable tin compound is initially added to the aqueous dispersion of the mixed-phase rutile pigment at a pH
value below 3 and the main amount is subsequently added and is hydrolyzed at a pH value above 10, whereafter the mineral acid solution of the antimony compound is added and is hydrolyzed at a pH value below 3.

18. An electrically conductive mixed-phase rutile pigment obtained according to the process of claim 9, 10, 11, 12, 13, 15 or 16, for dyeing and for imparting antistatic properties to plastics, synthetic fibers, laminated fibers, for producing electrically conductive adhesive compositions or for producing dyed paints having antistatic properties.