Note: Descriptions are shown in the official language in which they were submitted.
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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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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
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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~.
E5~Qa~_~
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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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.
~b~a~
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.
E ~
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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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
:~ , . . .
