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Патент USA US2131841

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Panacea, 1938
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2,131,841
UNITED ‘STATES PATENT OFFICE
PROCESSING OF CALCINEIl PIGMIENTS
Sanford C. Lyons, Bennington, Vt., asslgnor to
‘ Birdv Machine 00., Walpole, Mass, a corpora
tion of Massachusetts
,
- .
No Drawing.v Application May 10, 1937,
Serial No. 141,710
15 Claims.
(CL'134-—58)
This invention relates to the processing of
calcined pigments‘ with a ,view toward arriving
at a ?nished pigment product of such ?neness
of particle size, freedom ‘from water-soluble con5 taminations, and other qualities as to render such
"
.
Oxide in proportions 01?. Say, about 50% each
The ore is digested with strong sulphuric acid
serving to transform the mixed oxides into iron
and titanium sulphates. The cake ‘of mixed
iron and titanium sulphates thus Produced is 5
product eminently'useful- for various purposes,
for instance, in paints, lacquers, resins, and other
dissolved in water and the mixed salt solution
is then treated with scrap iron or its equivalent
compositions.‘
to reduce the ferric sulphate to ferrous sulphate
'
In producing pigments for use in paint and
10 lacquer compositions, it is customary tocalcine
the pigment particles, which are of extremely
?ne or_ colloidal particle size byv reason of their
previous formation through precipitation, so as
to develop particles or aggregates of su?iciently
is larger dimensions to aiford maximum opacity
or covering power. In this latter connection, it
might be noted» that, when a pigment, e; g.,
titanium dioxide, is formed through preeipita-
while the titanic sulphate is preserved largely as
such. After silica and other water-insoluble‘ im- 10
purities have been settled from the resulting
solution of ferrous sulphate and titanic sulphate, ~
the solution is ?ltered to produce a clear liquor
which is then heated to boiling for the purpose,
of causing the decomposition by hydrolysis of 15
the titanic sulphate into titanic hydroxide. ‘ The
titanic hydroxide is precipitated as extremely
?ne or colloidal particles,v a substantial fraction
_ tion, a substantial fraction of the pigment parof which are smaller than even the wave length
20 ticles are apt to be of unduly ?ne particle size, » of light just beyond the visible range, as already 20
namely, of a size less than the wave length of indicated. The precipitated titanic hydroxide is
light just beyond the visible range, e. g., a wave
length, 0.15, within the ultra-violet region, in
' washed free of iron salts during ?ltration or
afterwards; and the washing treatment may be
. consequence of which the pigment" does not ex" 25 hibit its maximum potential light-re?ecting or
so thoroughly performed {as to leave as little/as,‘
say, about 0.01% iron, calculated as oxide, in 25
covering property. 'It is for this latter reason
that pigment production includes a, calcining
operation, in the course of which the ultra-?ne
or colloidal pigment particles are caused to clus-
the washed product. Such residual .riron salt as
remains in the washed product is sometimes re
duced to soluble ferrous salt ‘by treatment ‘of
such product with suitable reducing agents, such
as hyposulphurous acid or hyposulphite contain- 30
ing, if desired, powdered zinc dust or its equiva
30 ter into aggregates distinctly larger than such
wave length of light just beyond the visible range.
Inasmuch as the growth of pigment particles
, during the calcining operation cannot be con-
trolled with precision or accuracy, it is invariably
lent, to accelerate the solubilization and decolori-_
zation of residual iron salt. After the decoloriz
ing treatment, the precipitated titanichydroxide
35 the case that the pigment emerging from the cal- may be washed and ?ltered from suspension in 35
cining. kiln‘ contains a substantial fraction of . the form of a thick paste or plastic mass ready
undesirably large pigment clusters or aggregates,
for the conventional calcining operation.‘
that is, clusters or aggregates so coarse and gritty
as to detract from the smoothness, homogeneity
Preparatory to calcining the precipitated ti
tanic hydroxide, it is desirable toadmix there
' 40 of texture, and covering power potentially realizable from the pigment.
,
‘
Theinvention hereof will be discussed in terms
of the processing of titanium dioxide as it emerges
from a calcining kiln, but it is to be understood
45 that the inventive principles hereof are applicable to other ‘pigments prepared by processes
inclusive oi." precipitating and calcining operations. Before entering into a discussion of the
with a suitable ?uxing agent, such as'potassium 40 ‘
carbonate, which promotes growth or aggregation
of the ultra-?ne or coloidal particles to sizes dis
,tinctly greater than the wave length of light
iustbeyond the visible range, as previously indi-‘
cated. This may be done by admixing with the 45
paste or plastic mass of titanic hydroxide su?i
cient potassium carbonate solution of appropri
ate strength to yield a thick slurry and removing
-~ invention hereof, it is perhaps helpful to'outline
free solution from the slurry to form a paste
the'prod'uction of titanium dioxide pigment up
'to_ ‘and including the precipit
‘g and calcining
for introduction‘into the calcining kiln. Dur
ing calcination, the titanic hydroxide‘ is substan
operations.
'
"
_
tially completelydehydrated as‘ the ?ne, ultra
The common sourcev of titanium dioxide pig- _‘ fine, and colloidal particles formclusters or ag
ment is the ore known as ilmenite, which‘is com-
'55v posed essentially of iron ‘oxides
g'regates of titanium dioxide of promiscuous sizes >
titanium‘, . distinctly greater-‘than the wave length of light :
J
2
2,131,841
within the ultra-violet region‘- wherefore, the cal
cined product emerging from the kiln consists
of titanium dioxide. pigment, a substantial frac
tion of whose particles are undesirably gritty
or oversized for lacquers, paints, and other com
positions. It is hence generally the custom to
reduce the calcined pigment as'an aqueous slurry
to ?ner particle size in a ball mill and to deliver
the ball-milled slurry to grading or. classifying
10 apparatus serviceable for resolving the slurry into
a ?ne pigment fraction for use in lacquers, paints, or the like and a relatively coarse or gritty pig
.ment fraction for retreatment in the ball mill.
' .' However, the grading or classifying apparatus
is used in prior art practice has not only been cum
bersome but-has been imperfect, so far as con
solids fraction emitted from the centrifuge con
tains entrained therein but an insignificant
amount of pigment particles of a size smaller
than about Z'microns. It is thus seen that the
centrifugal fractionating treatment performed
hereby on the ball-milled pigment slurry is a
highly selective one productive of a ?ne pigment
fraction sharply de?ned from the coarse or gritty
fraction with which it was originally associated.
The aqueous suspension of ?ne pigment par 10
ticles resulting from the centrifugal fractionat
ing treatment hereof may be subjected to suitable
treatment for the recovery of its pigment con
tent. Thus, when it is desirable or necessary
that the ?nished pigment be as free as possible
1s,
fromwater-soluble salts or other contaminations,
cerns yielding a ?ne pigment fraction with?the/ the aqueous suspension of ?ne pigment particles
may advantageously undergo the continuous elec
desired selectivity or freedom from oversizedip'ar
trophoretic centrifugating treatment described in
ticles. In other words, it has yielded ?ne pig
20 ment fractions whereingthere was still likely to be Lyons Patent No. 2,057,156, dated October 13, 1936. go 1
present considerable oversized or coarse pigment Such electrophoretic centrifugating treatment is
particles detracting from the smoothness, uni~ » centered‘ about the deposition of the pigment par
formity of texture, opacity or tinctorial power, ticles from aqueous suspension on a centrifuge
and other qualities desired in lacquers or paints wall under combined \electrophoretic and centrif
ugal forces and the progressive removal from the
26 whereinto such ?ne fractions entered.
In accordance with the present invention; the centrifuge wall of the solids thus deposited there
on as fresh suspension to be electrophoretically
calcined titanium oxide emerging from the cal
cining kiln is suspended in water to form a thick centrifuged is being progressively fed into the
suspension, preferably in the-substantial absence centrifuge. The ?ne pigment fraction thus re
covered from suspension as a moist plastic mass
80 of any dispersing agents. The resulting suspen
sion, which may well have a solids content of,
say. about 30% to 35%, is progressively fed into
a ball mill which reduces to ?ner particle size
a considerable portion of the oversized or gritty
pigment particles. The ball-milled suspension
progressively leaving the ball mill may be passed
35
as such or after dilution with water to a cen
may be dried, disintegrated. in a ball mill, ham
mermill, or equivalent instrumentality, and used
as such in making lacquer, paint, and other com
positions. The pigment product thus realized,
being composed essentially only of particles of a
size less than about 2 microns,is eminently adapt
ed for its intended purpose by reason of the
trifuge, preferably a continuous ?ow centrifuge smoothness, uniformity of texture, and high
of the type shown in Lyons application Serial No.
89,886, ?led July 10, i936, which centrifuge is
designed to receive at substantially constant rate
opacity or coveringpower in coatings or ?lms
wherein it appears,
40
suspension to be centrifuged as solids deposited
treatment of. the ball-milled slurry may be re
passed into the ball mill for further bail-milling‘
along with fresh slurry of calcined pigment fed 45
into .the ball mill. The fraction of coarse pig
ment returned to the ball mill may, of course,
vary, depending-upon the rate at which slurry
is being run-therethrough and the other condi
‘ The relatively coarse or oversized Pigment frac
or volume of ?ow an incoming stream of a solids - tion» resulting herein from ' the centrifugating
from suspension on the centrifuge wall are being
progressively emitted through one end of the
centrifuge and liquid .containing residual ?ner
solids in suspension or practically devoid of solids
is being emitted through the other end of the
centrifuge. As further stressed in this applica
tion, centrifugation is performed under substan
tially constant solids-depositing conditions, in
tions determinative of the grinding efficiency
thereof. Indeed, it is one of the advantages of the
cluding substantially constant effective centrifug- " instant invention that the conditions of opera
tion of the ball mill may be varied widely with
ing-force, since the solids deposited on the cen
trifuge wall are progressively removed during the outa?ecting the quality of the useful or fine‘
55 centrifuging operation and the rate-‘of flow of
vsuspension through the centrifuge and other sig
ni?cant factors are maintained substantially obn
pigment product pro¢h1cibl€hereby. It might be
noted that the e?luent' from the electrophoretic
centrifuge, which may contain some residue of
pigment suspended therein, may be reused at a
suitable stage in the method hereof, for instance, 0
operated under combined conditions conducive - be reused as the aqueous medium for suspending (w
’ to the progressive emission from the centrifuge of the titanium dioxide emerging from the calcining
kiln or be recycled» together with the relatively '
the oversized or gritty pigment particles,‘ pref
erably particles of a size greater than about 2 coarse or oversized pigment fraction into the ball
microns, while the liquid effluent from the cen
mill
In some instancesnit may be preferable to'“
66 trifuge consists of an aqueous suspension con
apply
other
steps
for recovering the ?ne'or useful:
taining the pigment particles of a size ?ner than
I about 2 microns but, nevertheless, = distinctly pigment fraction from the aqueous suspension of
greater than the wavelength of the light within the ?ne pigment fraction ._ produced by the
stant during the centrifuging operation. Accord
ant withthe instant invention, the centrifuge is
the ultra-violet region, as previously indicated.
70, It might be remarked that it‘ is possible to ensure
in the aqueous pigment suspension emitted from
‘the centrifuge substantial freedom from relatively
coarse and/or gritty pigment particles, that is.
‘ particles of a size of, say, 5 or 6 microns or‘greater,
a
whereas. on the other hand, the relatively coarse
centrifugating fractionating treatment hereof.
Thus,‘ such suspension4 may be treated with a '70
suitable pigment-?occulating agent, such as mag
nesium sulphate, in ‘amount controlled-to gen
erate pigment ?ocks 1 a size enabling substan-c
tially complete recovery 0 \such ?ocks‘by or
,
centrifuII-tion, as a distinguished from electro "16
3
r 2,131,841
phoretic centrifugation, by‘ ?ltration-on rotary coalesce into aggregates, as is true of the pigment
?lters, in ?lter presses, or the like’, while avoiding products which are derived from pigment sus
so far as possible excess ?ccculating agent whose pensions containing sodium silicate or like pig
substantially complete removal fromithe recovered ment dispersing agent and which may hence con
pigment solids may present some di?iculty. tain residual silica gel or like‘ cementitious ma
vApropos of treating the aqueous suspension of ?ne terial tending to bond together the pigment par
or useful pigment with a ‘pigment-?occulating ticles into undesirable aggregates. The method ‘
agent, it might be observed that, by reason of hereof presents the important advantage that, ‘
initially dispersing the pigment in water in the irrespective of variations in the pigment-calcining
substantial absence of pigment-dispersing agent, and ball-milling operations and variations in 10
such as sodium silicate, a minimum amount of; the ball-milled slurry, it may be controlled to give
?occulating agent is necessary for developing in predetermined or reproducible results, i. e., pig
the suspension readily recoverable pigment ?ocks;
ment fractions of a particular particle size or
and this means not only a saving in cost of
particle size range and hence particularly adapted
15 ?occulating agent but also greater freedom from
residual water-soluble v?occulating agent in the
for certain purposes.
pension by centrifugation or ?ltration.‘ ‘The fact
It-should be understood by those skilled in the
art that the principles of the instant invention
are applicable to the processing of other pigments
is that the'product thus recovered in the substan
or extenders, such as lithopone, zinc sulphide,
,?occulated pigment‘product recovered froznsus:
20 tially complete absenceof any rinsing with water,
contains ‘but a trace of water-soluble contamina
calcium sulphate, barium sulphate, etc., which, 20
like titanium dioxide, are prepared by processes
tion, insomuch that it ‘is useful for pigmenting
various arti?cial resins, such as the phenol
involving precipitation, calcination, and ball
formaldehyde resins and the urea resins, without
quired when they are used for pigmenting and/or
milling to acquire those qualities desired or re
I'imputable to water-soluble, ingredients in the
extending paints, lacquers, resins, and congeneric
compositions.‘ Accordingly,’ it is intended that
pigment. Again, the mere trace of water-soluble
the various pigments or extenders that are put
.25 causing the
discoloration ' therein frequently
15,
j through treatments similar to those employedjn
products hereof is insu?icient to induce settling‘ the preparation of titanium dioxide shall be con
tendency in lacquers, paints, or like compositions ‘ sidered as the equivalents of titanium dioxide and 30
into which they enter, as contrasted with the that the appended claims are to be construed as
marked settling tendency in paints, ‘lacquers, or being imbued with such equivalency even though
titanium dioxide may be the pigment set forth
~ the like in which there occurs pigment whose con
_ pigment-?occulating agent left in the pigment
tent of residual pigment-?occulating agent - is
relatively high. ~
_
'
The centrifugating fractionating treatment
performed herein for the ‘purpose of resolving the
slurry of ball-milled pigment into a coarse pig
ment fraction returnedv to the ball mill and a
relatively ?ne pigment fraction put to use aii'ords
important advantages over the gravitational hy
dro-separatory methods heretofore frequently‘
relied upon for separating pigments into ?ne arid
coarse pigment fractions. In the gravitational
hydro-separatory methods of the prior art, which
depend essentially upon natural gravitational
speci?cally therein.
I claim:
.
.
‘
consists of particles of a size smaller than the
wave length of visible light, an improved titanium
dioxide pigment capable of smoothly covering 40
surfaces with uniform texture and high opacity,‘
which comprises calcining said precipitated ti
tanic hydroxide and thereby transforming its
' subsidence of the coarse pigmentparticles, while
content of particles smaller than the wave length
of light just beyond the visible range into titani
um dioxide aggregates of distinctly larger size,
ball-milling the resulting calcined titanium diox~
the ?ne pigment (particles remain in suspension,
ide pigment in the presence of water to form a
it is virtually impossible to realize useful frac
35
1. A method of producing from precipitated
titanic hydroxide, part of whose solids content
pigment suspension, continuously centrifuging
tionation unless the pigment suspension is of rela- ” the resulting pigment‘ suspension under substan
tively low solids content, say, about 8 to 12%; and
‘even at such low solids content, it is usually the
case that. a dispersing agent, such as sodium
silicate, is added to the pigment suspension to
55 de?occulate the pigment particles and thereby to
‘reduce the viscosity of the suspension markedly
tially constant solids-depositing conditions, in
cluding substantially constant e?ective centrifug
ing force, to remove coarse pigment particles
while leaving the ?ne pigment particles in‘ sus
pension, and recovering the ?ne pigment particles 55
from ‘suspension as an improved titanium dioxide
pigment of substantially constant particle size
and to increase the rate of subsidence of the
coarse pigment particles. In the process hereof, characteristics throughout the centrifuging op, on the other ‘hand, it is possible to perform the eration.
'
.
2. A method of producing from precipitated
centrifugal fractionation of the calcined and ballmilledv pigment‘, suspensionj-at a solids content titanic hydroxide, part of whose solids content
markedly- greater than 12%, for instance, at a consists of particles of a size ‘smaller than the
solids content as high as 30% to 45%, without any wave length of visible light, an improved titanium dioxide pigment capable of smoothly covering
difficulty whatever in effecting a sharp’ or selec
65. tive resolution of the solids content of the sus
the surfaces .with uniform texture and high
pension into a ?ne fraction and a relatively opacity, which comprises calcining said precipi
tated titanic hydroxide and thereby transforming
coarse fraction,- even in the absence of any dis
persing agent whatever in the suspension: *Aside its content of particles smaller than the wave,
from the fact that Pigment suspension can be length of light just-beyond the visible range into
titanium dioxide aggregates of distinctly, larger 70
70 handled most economically at high solids con
" tent, by reason of the smaller amount of ‘water sizefball-milling the resulting calcined titanium
" passing through. the processing equipment, the dioxide pigment in the presence of water to form
absence of sodium silicate orxlike'pigment-dis
a pigment suspensio continuously centrifuging
‘ ' ‘ .' persing agent in the suspension ensures a finished
the resulting pigment suspension under substan
pigment'product- whose particles do not tendto
tially constant solids-depcsiging conditions, in
, 7,6.
4
2,181,841
tially constant solids-depositing conditions, in
cluding substantially constant e?ective centrifug
cluding substantially constant e?ectivecentrifug
ing force, to remove coarse pigment particles
while leaving the ?ne pigment particles in sus
_ pension, adding to the suspension of ?ne pigment
particles a ?occulating agent in amount su?icient
ing force, to remove pigment particles coarser
than about 2 microns while leaving the ?ner pig
ment particles in suspension, adding to the sus
pension of ?ner pigment particles at ?occulating
agent in amount su?icient to ?occulate such par
ticles, and recovering the ?occulated pigment
to ?occulate such particles, and recovering the
?occulated pigment particles from suspension as
as improved titanium dioxide pigment of substan
tially constant particle size characteristics
10 throughout the centrifuging operation.
particles from suspension as an improved titani
um dioxide pigment of substanttally constant 10
'
3. A method of producing from precipitated ‘particle size characteristics throughout the cen
- titanic hydroxide, part of whose solids content
consists of particles of a size smaller than the
wave length of visible light, an improved titanium
dioxide pigment capable of smoothly covering
surfaces with uniform texture and high opacity,
which comprises calcining said precipitated ti
tanic hydroxide and thereby transforming its
content of particles smaller than the wave length
of light just beyond the visible range into'titani
um dioxide aggregates of distinctly larger size,
ball-milling the resulting calcined titanium di
oxide pigment in the presence of water ‘to form
a pigment suspension,'continuously centrifuging
- the resulting pigment suspension under substan
-
trifuging operation.
,
Y
,
6. A method of producing from precipitated ti- '
tanic hydroxide, part of whose solids content con
sists of particles of a size smaller than the wave
length of visible light, an improved titanium di
oxide pigment capable of smoothly covering sur
faces with uniform texture and high opacity,
which comprises calcining said precipitated ti
tanic ‘hydroxide and thereby transforming its 20
content of particles smaller than the wave length
of light just beyond the visible range into titanium dioxide aggregates of distinctly larger size,
ball-milling the resulting calcined titanium di
oxide pigment in the presence of water to form a 25
tially constant solids-depositing conditions, in
cluding constant effective centrifuging force, to
thick pigment suspension, continuously centri
?ne-pigment particles in suspension, and recov
tions, including substantially constant effective
0 fuging the resulting pigment suspension under
'
remove coarse pigment particles while leaving the - substantially constant solids-depositing condi
30
ering the ?ne pigment particles ‘from suspension
under combined centrifugal and electrophoretic'
forces as an improved titanium dioxide pigment
of substantially constant particle size character
istics throughout the centrifugingoperation.
4. A method of producing from precipitated
titanic hydroxide, part of whose solids content
consists of particles of a size smaller than the
wave length of visible light, an improved titanium
dioxide pigment capable of smoothly covering
40 surfaces with uniform texture and high opacity,
which comprises calcining said precipitated ti
tanic hydroxide and thereby transforming its
' content of particles smaller than the wave length
of light just beyond the visible range into titani
um dioxide aggregates of distinctly larger size,
ball-milling the resulting calcined titanium di
oxide pigment in the presence of water to form
a pigment suspension substantially devoid of pig
meat-‘dispersing agent, continuously centrifuging
centrifuging force, and at a solids content mark-' 30
edly greater than about 12% to remove coarse
pigment particles ‘while leaving the ?ne pigment
particles in suspension, and recovering the ?ne
pigment particles from suspension as an, im
proved titanium dioxidepigment of substantially 35
constant particle size characteristics throughout
the‘ centrifuging operation.
'
7. A method of producing from precipitated
titanic hydroxide, part of whose solids content
consists of particles of a size smaller than the 40
wave length of visible light, an improved titanium
dioxide pigment capable of smoothly covering
surfaces with uniform texture and high opacity,
which comprises calcining said precipitated ti
tanic hydroxide and thereby transforming its
content of particles smaller than the wave length
of light just beyond the visible range into titanium
dioxide aggregates of ’ distinctly larger size, ball
milling the resulting calcined titanium dioxide
pigment in the presence of water-to form a thick 50
the
resulting
pigment
suspension
under
substan50
pigment suspension, continuously centrifuging the
tiall'y constant solids-depositing conditions, in
cluding constant e?ective centrifuging force, to
remove pigment particles coarser than about 2
microns while leavingthe ?ner pigment particles
, in suspension, and recovering the ?ner pigment
particles from suspension as an imprwed titani
um dioxide pigment of substantially constant par
‘ticle size characteristics throughout the cen
resulting pigment suspension under substantially
constant solids-depositing conditions, including ‘
substantially
constant
effective
centrifuging
force, and at a solids content markedly greater 65
than about -12% to remove pigment particles
coarser than about 2 microns while leaving the
?ner pigment particles in suspension, and recov
ering the ?ner pigment particles from suspension
trifuging operation.
as an improved titanium dioxide pigment of sub
5.
A
method
of
producing
from
precipitated
ti-‘
60
' tanic hydroxide, part of whose solids content stantially constant particle size characteristics
consists of particles of a size smaller than the
wave length of visible light, an improved titani-,
um dioxide pigment capable of smoothly cover
65 ing surfaces with uniform texture and high opac-_
ity, which comprises‘ calcining said precipitated
throughout the centrifuging operation.
_
8. A method of producing from precipitated
titanic hydroxide, part of whose solids content '
consists-of particles of a size smaller than the
wave length of visible light, an improved titanium
titanic hydroxide and thereby transforming its dioxide pigment capable of smoothly covering
content of particles-smaller than the wave length surfaces with uniform texture and high opa ,y,
which comprises calcining said precipitated ti
of light just beyond the visible range into titani
tanic hydroxide and thereby transforming its
70 um dioxide aggregates of distinctly larger size, content of particles smaller than the wave length 70
_
ed titanium di
‘9 ball-milling the resulting cal
oxide pigment inithe presence 0 water to form a of light just beyond thevisible range into titanium
pigment suspension. substantially devoid‘ of pig dioxide aggregates of distinctly larger size, ball
uncut-dispersing agent, continuously centrifuging milling the resulting calcined titanium dioxide
75 the resulting pigment suspension under substan- L pigment in the presence of water to form a thick
I
a
i
4'
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2,181,841
5
pigment suspension, continuously centrifuging the
resulting pigment suspension under substantially
constant solids-depositing‘ conditions, including
substantially constant effective centrifuging force,
dioxide pigment capable of smoothly covering
surfaces with uniform texture and high opacity,
which comprises calcining said precipitated ti
and at a solids content markedly greater than
about 12% to remove pigment ‘particles coarser
content of particles smaller than the wave length
of light just beyond the visible range into titanium
than about 2\microns while leaving the ?ner pig
ment particles in suspension, adding to the sus
milling the resulting calcined titanium dioxide
tanic hydroxide and thereby transforming its
dioxide aggregates of distinctly largersize, ball- -
pension of ?ner pigment particles a ?occulating - ‘ pigment in the presence of water to form a thick
10
agent-in amount sufficient to ?occulate such par
ticles, and recovering the ?occulated pigment par
ticles from suspension as an improved titanium
ing the resulting pigment suspension under sub
dioxide pigment of substantiallylconstant particle
stantially constant solids-depositing conditions,
including substantially constant effective centri
iuging force, and at a solids content markedly
size characteristics throughout ‘the centrifuging
15
pigment suspension substantially devoid of' pig 10
ment-dispersing agent, continuously centrifug
operation.
i
.
»
'
‘
9._A method of producing from precipitated
greater than about 12% to remove‘ pigment par
titanic hydroxide, part of whose solids content
consists of particles of a'size smaller vthan the
ticles coarser than about 2 microns while leav
hydroxide and thereby transforming its content
proved titanium dioxide pigment of substantially
constant particle‘size characteristics throughout
the centrifuging operation.
ing the ?ner pigment-particles in suspension,
v wave length of visible light, an improved titanium ,?occulating the ?ner pigment particles left in
20 dioxide pigment capable of smoothly covering suspension, ?ltering the‘?occulated pigment par 20
surfaces with uniform-texture and“ high opacity, ticles, drying the ?ltered pigmentmass, and
which comprises calcining said precipitated titanic disintegrating the dried mass to provide an im
of particles smaller than the wave length of light
just beyond the ‘ visible range into titanium di
oxide aggregates of distinctly-larger size, ball:
.milling the resulting calcined "titanium dioxide
pigment in the presence of water to form a thick
‘pigment suspension, continuously’ -.centrifuging
30
the resulting pigmentsuspensionunder substan
12. A method which comprises continuously
feeding calcined titanium oxide pigment and
'water through a ball mill while ball-milling such
pigment to produce an aqueous slurry containing
a pigment fraction of oversized particles and a 30
pigment fraction of the desired ?ne particles,
tially constant solids-depositing conditions, in
cluding substantially constant “effective centrie continuously centrifuging the aqueous slurry of
fuging force, and at a solids content‘vimarkedly ' ball-milled pigment under substantially constant
greater than about-12% to remove pigment par
solids-depositing conditions. including substan
35 ticles coarser than about 2 microns while leav
tially constant effective centrifuging force,"to‘ re 35
ing the ?ner pigment particles in suspension, and . move continuously therefromthe pigment frac
recovering the ?ner pigment vparticles from sus
tion of oversized particles and to produce con-.
pension under combined centrifugal and electro vtinuously‘ia.suspension ‘of an improved titanium
phoretic forces as an improved titanium, dioxide dioxide pigment of substantially constant par
pigment of substantially-constant 'particle3size ,ticle'size characteristics throughout the centri 40
characteristics throughout the centrifuging fo -
fuging operation and continuously feedingv sub
‘stantially only such removed pigment fraction to
10. A method of producing from precipitated,‘ gether withi‘newly ‘calcined titanium oxide pig
titanic 'hydroxide, part ,of whose solids content ment.‘ and water being fed through the'ball mill.
consists of particles of a size smallerlthan the
13. A, method which comprises continuously 45
wave length of visible light, an improved titanium feeding- calcined titanium ‘oxide ‘,pigment and
eration.
-
.
i
'
dioxide pigment capable of smoothly covering sur-" _‘ water? "through'la ball mill while- ball-milling
faces with uniform texture and high opacity‘,
suchpigment to produce an aqueous slurry con
> which comprises calcining said precipitated tie’ I ‘tai'riihgaa pigment fraction of oversized parti
50 tanic hydroxide and thereby transforming its; ,‘cles and a ,pignient fraction of the desired ?ne 50
content of particles smaller than the wave length - particles,v continuously centrifuging the aqueous
‘of light just beyond the‘ visible range into titanium 1' slurry ‘of ball-milled pigment under substantially
dioxide aggregates of distinctly larger size, ball- ' constant ‘solidsédepositing conditions, including
milling the resulting calcined titanium dioxide
substantially constant effective‘ centrifuging force,
55 pigment in the presence of water to form a thick
and at a solids content of about} 30% to 45% ‘to
pigment suspension substantially devoid of pig . remove continuously therefrom the pigment frac
tion of oversized particles .and to produce con‘
ment-dispersing agent, continuously<centrifuging
the resulting pigment suspension under substan
tinuously a suspension of an improved titanium
tially constant solids-depositing conditions, in~ dioxide pigment of substantially constant par
ticle size characteristics throughout the centri 60
60 eluding substantially constant e?ective ‘centri
fuging force, and at a solids content-markedly fuging operation and continuously feeding sub
greater than about 12% to remove pigment par
stantially only such removed pigment fraction toe
ticles coarser than about 2 microns while leav-"v gether with newly calcined titanium oxide‘pig
ing the ?ner pigment particles in suspension,
65 ?occulating the ?ner pigment particles left in
suspension, dewatering the ?occulated pigment
ment and water being fed through the ball mill.
14. A‘ method which comprises continuously 65
feeding calcined titanium oxide pigment and
particles to substantial dryness, and disintegrat- v water through a ball mill while ball-milling such
ing the dried pigment mass to provide an im
pigment to produce an aqueous slurry containing
proved titanium dioxide pigment of substantially
70 constant size characteristics throughout the cen
trifuging operation.
‘
,
Q
upwards of about 30% solids as both a pigment
fraction of oversized particles and a pigment frac
m
tion of the desired ?ne particles, continuously
centrifuging the aqueous slurry of ball-milled pig
titanic hydroxide, part of whose solids content ment under substantially constant solids-deposit
consists of particles of a size smaller than the, ing conditions, including substantially constant.
76 wave length of visible light, an improved titanium e?ective centrifuging force, and at a solids con-‘ 75
11. A method of producing from precipitated
6
2,181,841
tent upwards of about 30% to remove continuous
1y therefrom the pigment fraction of oversized
particles and to produce continuously a suspen
sion of an improvedtitanium dioxide pigment of
substantially'consta'nt particle size characteris
tics throughout the centrifuging operation and
continuously feeding substantially only such re
moved pigment fraction together with newly cal-_
cined titanium oxide pigment and water being
10 fed through the ball mill.
'
15.- A method which comprises continuously
'feeding calcined titanium oxide pigment and
water through a ball mill while ball-milling such
pigment to produce an aqueous slurry containing
15 upwards of about 30% solids as both a pigment
fraction of oversized particles and a pigment frac
tion of the desired ?ne particles, continuously
centrifuging the aqueous slurry of ball-milled pig
ment under substantially constant solids-deposit
ing conditions, including substantially constant
‘ effective centrifuging force, and at a solids con
tent of about 30% to 45% to remove continuously
therefrom the‘pigment fraction of oversized par
ticles and to produce continuously a suspension
of an improved titanium dioxide pigment of sub
stantially constant particle size- characteristics 10
throughout the centrifuging operation, and con
tinuously feeding substantially only such removed
fraction together with newly calcined titanium
oxide pigment and water being passed through the
15
ball mill.
SANFORD C. LYONS.
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