Note: Descriptions are shown in the official language in which they were submitted.
~96~0'7
Ds 28997
This lnvention relates to chrome plement~ of improv~d ~ulphur
dioxide resistAnce and hi8h glo~s a~d to a method for their manufacture.
Accordi~g to the invention there i~ provided a process ~or
the manufacture of an ~mproved chrome yellow p~gment ~hich comprises
the simultaneous treatmont of an aqueous suspension of a chrome
yellow pigment w~th two treating a~ents which are (1) metaphosphoric
acid or a water-~oluble 6alt thereof snd (ii) a water-601ub~e cerous
s~lt.
As chrome yellow plgments there are meant lead chromate yellow
piBments such as primrose chromes, lemon chroms~ and middle chromee.
As water-soluble cerous s~lts there may be mentioned
for example cerous chloride, cerous sulphate, c~rous nitrate and
cerous acetate.
As water-soluble metaphosphate~ thcre may be mentioned for
example sodium and potassium metaphosphate~ and metapho~phoric acid, but
other water ~oluble salt~ may b0 used if desired. It is preferred to u~e
a ~alt rnther than the free acid.
The process oi thé in~ention ~may be carried out con~eniently
by adding an aqueous solution of the watsr-soluble cerous salt or water-
soluble metaphosphate gradually with ~tirring to a 6uspension of the
pigment in an aqueous solution of the other water-soluble
treatlng agent and, preferably after ~tirring for a further ~hort
time, collecting the treated pigment by for example filtration, washing with
watar, and drying, for example by heatin8 in air at 70C~ It iB
however, preferred to add the two treating agents gradually and 6~mu1taneou~1y,
preferably at substanti~lly equivalent rate~, to a stirred aqueou~ 6uspension
of the p~gment.
P~gments of particulArly good sulphur dioxide resistance are
obtained if the water-~oluble cerou~ salt and the water-soluble
-- 2 - i
-`
1~961(~'7
Ds 28997
metaphosphate are added to a stirred aqueous suspension of chrome
pigment at approximately equivalent rates. It is however sometimes
advantageous to add a minor portion, such as 10% , of the water
soluble metaphosphate before commencing addition of the water-soluble
cerous salt since the metaphosphate may act as a dispersing agent
on the pig.nent.
The addition of the water-soluble cerous salt and of the
water-soluble metaphosphate should desirably be carried out over a
period of at least 15 minutes. Shorter periods may give non~uniform
treatment of the pigment particles. Periods longer than 30 minutes
do not in general offer significant advantage.
The treatment may be carried out on the slurry of the
pigment obtained directly from, for example, a solution of sodium
dichrom~te, sodium sulphate and sodium hydroxide and a lead nitrate
solution, but a slightly superior product is obtained if the
untreated piement is isolated, washed with water and then
reslurried for treatment.
The treatment is preferably carried out at a temperature
between 60 and ~0C but other temperatures outside this range may
be used if desired.
The amount of water-soluble cerous salt and of water-
soluble metapllosphate ar~ proferably chosen to be roughly equivalent
although a moderate excess of either will not nor~ally be
deleterious, and to be sufficient tG provide cerous metaphosphate
~096~0 7
Ds 28997
in amount between O.S and 20%, and more preferably between 3 and 12%
of the weight of untreated pigment.
The product of the process of invention is a chrome
pigment each particle of which is coated with insoluble cerous
metaphosphate which affords protection to the pigment against attack
by atmospheric sulphur dioxide. This coated pi6ment is also a
feature o the invention.
It is desirable to maintain the pl~ of the suspension
at a suitable value, not only because of the well-known instability
o~ chrome pigments in solutions of very low or very high pH, but
because unsatisfactory coatings may be obtained at unsuitable pH
values. At low pH precipitation may be incomplete and at high pU
the cerium may be precipitated as hydrated oxide instead of as
meta-phosphate. The preferred pH range is 6-8,5. The pH may~be
ad~usted to this range by the addition as necessary of dilute acid
or dilute alkali or of acidic or alkaline salts.
The process of the invention may be used in conjunction
with other known methods for improving the properties of chrome
pigments, It may, for example, precede, or preferably, follow .
t~eatment of the pigment to deposit coatings of oxides of metals
such as aluminium, cerium, titanium, tin, antimony, manganese or
silicon on the pigment.
The pigments so treated may be isolated and dried
by conventional means, including for example drying in vacuo.
- 4 -
109610 7 Ds 28997
By th~ procees of the inYentlon pigmenta are obtained which
are o~ impro~ed sulphur dioxide resistance ~hen incorporated into paint
media, for example alkyd based and acrylic based paints. Thoy also show
An adva~tage in superior gloss o~er other treatments which provide 8
comparable ~mpro~enent in sulphur dioxide re~istance.
Tho ~ollowing description ProYides two examples of the present
invention and comparisons Or these with five pigments that are either
uncoated or are coated with salts that ar~ closely related to cerous
metaphosphate. In the description all tha parts and percentageo are
by weight. All the examples and pigments are prepared from the same
pigment suspension.
Pi~ment Suspension
An untreated lemon yellow shade chrome pigment is prepared
by the ~ollowing procedure.
A solution Or 219 parts Or sodium dichromate dihydrate,
93.75 parts of anhydrous sodium sulphate, 18~.75 parts of sodium
chloride and 210 parts of aqueous sodium hydroxide (6peciric gravity
1.35) in 2700 part8 of water i8 added over about 30 ~inute~ with
stirrin6 to 6000 parts of 0.4 mol~r lead nitrate solution at pH 4
and 20C until tho soluble lead is reduced to 0.014 molar and the pH
ra~sed to 5.2 - 5.4. Iho p~ is then raised to 5.8 by add~tion o~
aqueous sodium carbonate and the slurry heated at 70C for one hour,
diluted with water to 18,0Q0 parts and allowed to settle for 18 hours.
The supernatant liquid is re~oved by decantation and the residual
durry diluted to 10,000 parts and heated to 70C. 10~ Sulphuric
acld i8 added to bring the p~ to 2.6 followed by a solution of 21
parts Or sodium sulphate in 100 parts of water and 20% aqueous
- 5 -
.
.
i
1096~ D~3 28997
sodium carbonate to bring the pH to 5.5. lOt> Parts of aqueous so~um
silicate (containing 24.8% silicon as SiO2 and 9.296 sodium as Na20) diluted
to 250 parts is added over 15-20 minutes followed by a solution of 105
part~ of ammonium sulphate in 500 parts of water over 30 minutes. A m~xture
Or 21 parts of antimonous oxide, 21 parts of citric acid and 60 parts
of concentrated hydrochlor$c acid ~ then added over 10 minutes followed
by 20% aqueous 60dium carbonate to bring the pH to 7Ø I~e suspension,
which conta~ns about 750 parts of pigment, is stirred for 10 minutes. Thi6
suspen~ion iB used for providing treated and untreated pigments as described
below.
Pi~ment 1, untreated p$gment ~or comparison purpo~es, iB obtained by
filtration and washing with water of a portion of the Pigment Suspension
which iB then dried at 70-90 C.
Pigments 2 to 5 and Examples 1 and 2 are obtained by adding solution~ ~
f cerium 6alts and phosphates as described below at approximately ¦ --
equivalent rates over about 15 minutes to stirred portions of the
Pigment SuspenRion, prepared as described above, each portion containing
about 190 parts Or pigme~t at p~l 7.0 and about 70C. l~ne treated
pigment~ are isolated by filtration, washing w~th water, and drying
at 70-90C.
PiRment 2 32.3 Parts of 20% ceric sulphate liquor and 8.2 parts of
~odium orthophosphate, each in 250 p~rts of water.
Pif~ment 3 18.5 Parts of cerous nitrate hexahydPate and 7 parts
of 60dium orthophosphate, each in 250 parts of water.
-
~, ..... .. . . .
Ds 28997
Pi ment 4. 37.6 Part~ of 20% ceric ~ulphate liquor and 9.0 parts
of 60dium metaphosphate, each in 250 partG of water.
PiRment 5 14.8 Part~ of calcium chloride and 10.4 parts of
sodium metaphosphate, each in 250 parts of water.
Exam~le 1
11.6 Parts of cerou~ nitrate hexahydrate and 8.2 parts of sodium
Rletaphosphate each in 250 part8 of water.
l~cample 2
23.2 Parts of cerous nitrate hexahydrate an* 16.4 parts of aodium
metaphosphate, each in 250 part~ of ~ater.
l~cample 1 and Pigments 2-5 illustrate pigments having a coating of
about 5% by weight of phosphate, and Example 2 illustrates a pigment having a
coating of about 10~ by weight of phosphate. Pigoent 1 illustrates a pigment
~/hich has not been coated with either cerium or phosphate. Only Examples 1
1~ and 2 illustrate treated pigment of the ~nvention, Pigents 1-5 being
described for the purposes of the following comparisons. ;
Com~arison 1
Treated pigments prepared as described in Examples 1 and 2 and
Pigment~ 2-5 and untreated pigment (Pigment 1) are each incorporated into
a pa~nt by the following ~rocedure.
28 g. of pigment, 23.4 g. of a 20X Rolution of an alkyd re6in in
xylene and 125 g. of 3 mm. Ballotini beads are placed in a 4 oz. glAss bottle
and shaken for 30 minutes. After separation from the beads the mixture i8
blended with 70.8 g. of a 50% eolution of allcyd resin in xylene and 18.8
of a butylated melamine ~ormaldehyde re6in. The blend ~8 applied in a coating
o~ thickness 0.01 inch ontO a primed metal panel and the coating dried in alr
for 30 mlnutes and then heated in an oven at 120C for 30 minutes.
The coating6 of the paints are te~ted for sulphur dioxide resistance
in a Kesternich apparatus by the procedure of the Glerman standard method for
-7-
1096~ 7
paint panels (DIN 50018). D~ 111./73
The following results are obtained:-
Pigment SamDle 3 Cycles 5 Cycles
Pigment 1 (Control) 2 1-2
5Example 1 4 4
Example 2 4-5 4-5
P$gment 2 2 1-2
3 4~5 1-2
~ 4 1-2 1
10 " 5 4_5 4_5
The resistance is expressed on a scale of 1 to 5, 1 representing
complete destruction of colour and S no change. Only Examples 1 and 5
afford a considerable measure of protection against sulphur dioxide.
Compari~on 2
Paint coatings prepared as described in Compari~on 1 are J
tested for gloss by the method of ASTM Spec. D523 using a specular ~i
gloss meter at an angle of 20 with a setting for black glass of 88% reflectance. ,
The difference in reflectance between the samples of
paints from treated pigments and from untreated, pigment (Pigment 1), expressed
20 as percentage ren ectance are as follows:-
Example 1 ~ 12
2 ~ 10
Pigment 2 ~ 18
Pigment ~ + 18
Pie~ent 4 +
Plgment 5 + 3
Thu8 although calciu~metaphosphate prov$des a similar impro~ement to cerous meta-
pho~phate in sulphur dioxlde and-both cerou8 and ceric metaphosphate~ pro~ide~
improved eloss only cerous ~etaphosphate pro~ides a reasonable measure of
impro~ement ~n both glosg and sulphur dioxide resiRtance.
-- 8 --
