Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a material. In a particu-
lar aspect this invention relates to hollow microspheres.
It is known to make hollow microspheres by the pro-
cess of U.S. Patent No. 3,796,777, the prior art disclosed
therein, and U.S. Patent Nos. 2,7~7,201; 2,978,3~0;
3,030,215 and 3,699,050.
However, various of the prior art processes have
difficulties such as producing ammonia as a pollutant.
The present invention provides a hollow microsphere
wherein the inner portion of the shell of which comprises
the reaction product of a silicate and a first insolubil-
izing agent, the outer portion of the shell oF which com-
prises the reaction product of a silicate and a second
insolubilizing agent and wherein the equivalent ratio of
silicate to, respectively, the first and second insolubil-
izing agent is less in respect of said inner portion than
said outer portion.
Preferably the silicate is selected from -the group
consisting of sodium and potassium silicate.
Preferably the first insolubilizing agent is an
acid.
Preferably the acid is selected from the group con-
sisting of boric and phosphoric acid.
Preferably the second insolubilizing agent is sel-
ected from the group consisting of acids and salts capable
of reacting with the silicate to form an insoluble reac-
tion product.
Preferably said salts are selected from the group
consisting of calcium salts, magnesium salts, aluminum
,JLi~'', .~"'~ ''.
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~!~J
salts and salts of polyvalent metals capable of reacting
with the silicate to form an insoluble reaction product.
Preferably the second insolubilizing agent is
selected from the group consisting of boric and phosphoric
5. acid.
In one înstance the second insolubilizing agent is
different to the ~irst insolubilizing agent.
Preferably the first and the second insolubilizing
agents are the same.
Preferably the equivalent ratio of the silicate to
the first insolubilizing agent in the inner portion is
such that unreacted silicate remains therein.
Preferably the equiva'lent ratio of the silicate to
the second insolubili~ing agent in the outer portiorl is
such that substantially no unreacted silicate remains
therein.
Preferably the second insolubilizing agent is present
in said shell to a depth oF not more than 50% thereof or,
more preferably, not more than 25%.
Preferably the silicate is sodium silicate, wherein
the first and second insolubilizing agents are both boric
acid and wherein the weight ratio of silicate to second
insolubilizing agent in the outer portion, expressed as
Na20:b203, is from 1.6-3:1 preferably 1.8-2.4:1 and most
preferab'ly about 2:1.
Preferably said shell contains an hydroxylated and/or
an oxygenated organic compound.
Preferably said compound is ethylene glycol diaceta-te.
Preferably the microspheres have an effective
density of 0.18-0.21 gm/cc, a size of 10-200micron, a shell
wall thickness of 1-2micron and a crush resistance of
150~1500 psc.
Preferably the'microspheres have a silane or a
siloxane~on the surface thereof.
The present invention also provides a process for
producing hollow microspheres comprisinq ~orming a fee~stock
JZ60
4 ~ 3~
containing water, a silicate and a first insolubilizing
agent, spray drying the feedstock to form hollow micro-
spheres and applying to the hollow microspheres so
formed a second insolubilizing agent whereby to produce
hollow microspheres the inner po.rtion of the shell of
which comprises the reaction product of the silicate and
the first insolubilizing agent, the outer portionoF which
comprises the reaction product of the silicate and the
second insolubilizing agent and wherein the equivalent
ratio of silicate to, respec-tively the first and second
insolubilizing agent is less in respect of said inner
por~ion than said outer portion.
.,
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~ 5.
.
In a preferred aspect the present invention provides
a process for producing hollow microspheres comprising
a. mixing together an aqueous solution ~i) contain-
ing a silicate and an aqueous solution (ii) contain-
ing a first insolubilizing agent to form a feedstock,
b. forming the feedstock into droplets and drying
the droplets to form hollow microspheres, an~
c. applying to the droplèts and/or the m;crospheres
so formed an aqueous solution (iii) of a second
insolubilizing agent whereby to produce hollow micro-
spheres the inner port.ion of the shell of which
comprises the reaction product of the silicate and
the-First insolubili7ing agent, the outer portion of
which comprises the reaction product of the silicate
and the second insolubilizing agent and wherein the
equivalent ratio of silicate to 9 respectively the
first and second insolubiljzing agent is less in
respect of said in~er portion than said outer poxtion
Solutions of alkali metal silicate are useFul in
the process of our invention. Alkali metal silicate solu-
tions are well known articles of commerce usually prepared
by dissolving the glass that results from the fusion of
a source of alkali metal and sand. Such solutions can
also be prepared by dissolving silica ir, an alkali metal
hydroxide. Useful silicate solutions contain about 1.5
to 4.0 moles-of SiO2 per mole of M20 and 25 to 55% w/w of
solids wherein M stands for an alkali metal. We prefer
to use sodium or:potassium silicate that contains 1.7 to
3.5 moles of SiO2 per mole of Na20 or K20 9 more preferably
2.0-3.2 moles of SiO2 per mole of Na20 or K20.
The potassium or sodium silicate is preferably
present in solution (i) as 25-55% by weight with about
40% by weight being more pre~erred.
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Solution (i) is preferably delivered to the mixing
step (a) a-t a temperature of from 5 -to 80C with 20-60C
being more preferred and 30-~0C being most preferred.
Boric acid is preferably present in solu-tion (ii)~
as 3-20% by weignt with 6-12% being more preferred. Solu-
tion (ii) is preferably delivered to the mixin3 step (a)
at a temperature of from 10-90C with 40-70C being more
preferred and 50-60C being most preferred.
It is preferred to add a solution, (iv) to solution
(ii) prior to mixing step (a) and that addition preferably
occurs immediately before mixing step (a).
The insolubilizing agent can be any acid which9 when
added to a silicate solution forms a relatively stable
solution that can be spray dried to form a hollow micro-
sphere; said microsphere having a solubility in water -that
is substantially reduced from that of the starting sili-
cate. These insolubilizing agents include acids such as
boric acid or phosphoric acid. We prefer boric acid. In
some embodiments of our inven-tion the insolubilizing agent
sprayed onto the surface of the formed hollow microspheres
or its precursor droplets can be different from that util-
ized in the bulk of the microsphere shell. These agents
which can be sprayed as solutions onto the droplets or
microspheres at any time after -they are formed can include
boric acid, phosphoric acid, calcium salts~ magnesium
salts, and aluminum salts, amony other polyvalent metal
salts that react to form insoluble reaction products with
silicates.
Another preferred embodiment of our invention in-
volves the addition of a water-miscible, high-molecular-
weight organic compound to the feedstock to be spray
dried~ Such organic compounds are desirably stable in
highly alkaline systems and not cause the silicate to gel.
In general, organic compounds that contain a number of
hydroxyl groups and/or exposed oxygens are useful. Exam-
ples of useful materials include cellosolve*, ethyl cello-
solve*, ethylene glycol, and ethylene glycol diacetate
(EGDA).
Trademarks
-- 6
. ,,
We prefer to use EGDA.
Solution (iv) preferably contains ethylene glycol
diacetate (EGDA) and solution (iii) may be 100% composed
of EGDA.
Solution (iv) is preferably added to solution (ii)
in the ratio range 100:0.1 - 100:3 with 100:0.5 - 100:2.0
being most preferred.
The ratio range of solution (i) to solution (ii) is
preferably 100:40 - 100:200 with 100:60 - 100:110 being
more preferred.
Mixing step (a) should preFerably be undertaken with
considerable care to avoid undesirable formation of gel.
Applicants recommend that mixing step (a) be performed
using a high shearing mixer. As an example, for a mixing
process using a 1000 litre mixing ~essel a mixer was used
having a primary disc of 75mm diameter and a secondary
disc of 225 mm diameter both driven on a single shaft at
3000rpm by a 10HP motor and with a disc immersion depth
of 640mm.
The feestock is preferably held for 1-2 hours after
mixing stèp (a) but it is preferred that it is not held
for more than 4 hours.
The feedstock is preferably held at 5-80C with
10-~0C being most preferred.
2~5 The feedstock preferably has a viscosity of 10-200
centipoise with 20-150 centipoise being more preferred.
Viscosity was measured using a Brookfiel~ RT Spindle No.1
at 100rpm viscometer.
The drying of the droplets is preferably conducted
in a chamber after spraying the feedstock into small
droplets. Such spraying may be done by impinging the
feedstock onto a rapidly spinning disc but is preferably
done by passing thP Feedstock through one or more spray
nozzles.
To dry the droplets hot air is pre-ferably passed
into the chamber at a temperature and in an amount sufficient
to effect drying. In general it is preferred that the hot
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8.
air inlets at 100-500~ with 200-300C being more preferred,
and exits at 60-160 C, more preferably 80-120C.
The hot air is preferably directed to introduce
substantial turbulence in the stream of droplets as this
can help in avoiclance of localized overheating and particle
marriage.
After spray drying the particles formed may be further
dried. Such durther drying is preferably achieved in an
oven at a preferred temperature of from 80-140C, more
preferably 90-110C at a particle inlet, and 120-250C,
more preferably 150-200C at a particle outlet. A preferred
oven is a rotating kiln. A preferred residence time for
partic1es in the oven is 10-80 minutes; more preferably
20-30 minutes.
After further drying, if that operation is performed,
the particles are preferably coated with siloxane or silane
using a solvent such as methylene chloride and preferably
by spraying. The coating is preferably carried out in a
mixer at 80-200C with 120-150C being more preferred, and
with a preferred residence time of 10-60 minutes, more
preferably 20-60 minutes.
The partic~les may be given a surface treatment in
a mixer by building up temperature from a starting point
of 80-200C, more preferably 120-150C, to 150-300C more
preferably 200-250C. That surface treatment is preferably
performed over a period of at least lU minutes.
The application of solution (iii~ preferably occurs
immediately after formation of the droplets and preferably
before completion of drying thereof but may occur later
such as during the further drying referred to above or
later.
We have found it to be chemically most efficient to
apply solution (iii) to the droplets but energy most effi-
cient if it is applied in the further drying.
Solution (iii) is preferably applied by spraying.
A suitable solution for spraying has substantially the
same composition as solution (ii) and additionally
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9.
preferably contains EGDA but may have a higher concentration
of boric acid and/or EGDA. Such a solution is preferably
applied in the weight ratio range to the feedstock of
2:100-50:100 more preFerably 10:100-30:100.
Solution (iii) applied during the spray drying should
preferably be applied under conditions avoiding flash
evaporation. Flash evaporation problems can be reduced
iF solution (iii) is sprayed in close proximity to the
initiation of the spray of droplets. Alternatively, by
introducing solution (iii) into a relatively cool region
of the spray drying step flash evaporation may be reduced.
A construction of preferred apparatus useful in
performing the method of this invention and its manner of
use will now be described with the aid of the accompanying
drawings in which:
Figures 1 and 2 are schematic representations of
the apparatus.
Figures 1 and 2 should be viewed together with
Figure 1 on the left and Figure 2 on the right.
The apparatus as described below is suitable For
production of 10-50kg of product per hour. If a larger
or smaller plant is required, sizes given should be adjusted.
The apparatus includes a 1000 litre first mixing
tank 1 for initially containing a solution (I) containing
2~ a potassium or sodium silicate and a 1000 litre second
mixing tank 2 for initially containing a solution (II)
containing boric acid.
lanks 1 and 2 are provided with stirrers 21 and 22
and tank 1 is provided with a high shear stirrer 230
In use a solution (III~ consisting of EGDA is added
to tank 2 and tank 2 is used to feed its contents via line
24 to tank 1 while mixing with the high shear stirrer 23.
Tanks 1 and 2 are provided with heat1ng 3ackets 26
and 27.
The contents of tank I, feedstock, after mixing are
carried by line 28 to a 1000 litre third tank 29 where they
are held until required. Tank 29 has a heating jacket 30
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10 .
and a mixer 25.
From tank 29 the ~eedstock is delivered by lines 31
and 32 via a high pressure pump 33 regulator 35 and a gauge
34 to a spray drier 36.
The spray drier 36 comprises a cylindrical portion
37 of 3300mm height and 2100mm diameter, a top frusto-cone
38 of 200mm height and a bottom frusto-cone 39 of 1210mm
height.
The spray drier 36 also includes an air inlet 41,
an air and particle outlet 42, a swirl chamber 43 in which
entering air is caused to swirl by means o~ a scroll 4~
and a descending tube 46. The chamber 43 has a height of
500mm and a diameter 40% of that of the cylindrical portion
37. The tube ~6 has a lPngth of 700mm.
Line 32 is connected to a spray nozzle head 47 (alter-
natively the head 47 may be replaced by a rotary disc
atomizer ~r a spray head having additional side exit nozzles).
An additional spray nozzle head 48 ancl supply line 50
therefor is optionally positioned in the spray drier 36.
The outlet 42 of the spray drier 36 is connected to
a cyclone 45 which has a fan 49~ an air outlet 51 which
passes to a dust collector (not shown) a rotary valve 5?
and an outlet line 55 to a rotary kiln 53.
The kiln 53 has a spray nozzle head 54 and supply
line 56 therefor and a heater 57 for blowing hot air into
the kiln. The head 54 and line 56 are optional.
Particles exit from the kiln 53 at 58 and are passed
to a first surface treatment mixer 59.
The mixer 59 has insulation 61, paddles 62~ and spray
nozzles 63 through which siloxane or silane is sprayed. A
heat source, not shown, is used to supply heat as indicated
- by arrows 64. An alternative position for spray nozzle
head 54 is in mixer 59 (kiln 53 or spray drier 361.
After treatment in the mixer 59 particles are passed
to a second surface treatment mixer 66.
Mixer 66 has insulation 67 and paddles 68. A heat
source, not shown, is used to supply heat as indicated by
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ll .
arrows 69.
After treatment in the mixer 66 particles are passed
to screening and bagging apparatus indicated by 71.
The present invention will be Further illustrated
by the following Examples. In the Examples, all parts are
by weight unless otherwise specified.
Example I
A solution (I) of 440 parts of sodium silicate NA45
were heated to 35C in tank 1.
NA45 is a sodium silicate produced by ICI Australia.
It has an Intermediate classification, sodium silicate of
mean weight ratio S102:Na20 of 2;75:1 and has a typical
analysis of % by weight of 10.8 Na20, 29.7 S102 and 40.5
solids. It has a specific gravity of 1.45 and a typical
viscosity of 200cp at 20C.
A solution (II) of 350 parts water, 31 parts boric
acid and 2.2 parts by weight EGDA were dissolved and blended
in tank 2 and heated to 60C~
20 parts of sollltion (II) were fed to tank 1 under
high shear mixing conditions at a rate of 2 parts per
minute. A -further 326 parts of solution (II) were fed to
tank 1 under the same mixing conditions at a rate of 8 parts
per minute. The final 37.5 parts of solution (II) were
then fed to tank 1 at a rate of 2 parts per minute.
Mixing was maintained in tank 1 for a further 5
minutes and the resultant feedstock was then pumped to
tank 29 where it was cooled to 20C.
The feedstock was then pumped at 1500psi to the spray
nozzle head 47. Spray nozzle head 47 had three orifices
of size 0.020 inch with flat top cores with two grooves
of 0.016 inch width and 0.024 inch depth.
The air temperature at the spray drier air inlet 41
was 350C and at the outlet 42 was 105C.
In the spray drier the spray nozzle head 48 w~s
supplied at 750-lOOOOpsi with a 60C solution (III) contain-
ing 8.8 parts boric acid, 100 parts water and 0.62 parts
EGDA.
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12.
The product exiting from the outlet 42 was hollow
spherical particles and those particles were fed via the
cyclone 45 to the ki'ln 53.
The kiln 53 was maintained at 90C at the particle
inlet and 195C at the particle outlet.
Particles exiting from the kiln 53 were passed to
the mixer 59 and sprayed with a 6.67% by weight solution
of Dow Corning 1107 Siloxane in ethylene chloride while
applying heat.
Particles were then passed from the mixer 59 to the
mixer 66 where the temperature was built up to 250C for
30 minutes.
The particles were then screened through an 80 mesh
sieve and packed.
The particles obtained by the above process were
microspheres which were clean, hollow, free flowing,
moisture r'esistant, effective particle density of 0.18-
0.21gm/cc. The particles ranged in size from 10-200 micron
and had a ~all thickness of 1-2 micron. Crush resistance
was in the range 150-1500psi.
By ranging the conditions microspheres haviny higher
density or different wall thickness can be obtained
The particles were suitable ~or use as a high volume
extender for resins and binders and in plastics mouldings
to produce low density finished products.
Example II
Example I was repeated excepting that the spray nozzle
head 48 was not used and in lieu the spray nozzle head 54
was used to spray the 60C solution containing 8.8 parts
boric acid, 100 parts water and 0.62 parts EGDA.
Results obt'ained were satisfactory and although the
particles were not of as good quality significant heat
saving in spray drier 36 was achieved.
Example III
Example I was repeated excepting that solution ~III)
was replaced (a) entirely by an equivalent amount of phos-
phoric acid, (b) in part and entirely by (i) aluminium
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salts, (ii) calcium salts and (iii) magnesium salts and
(c) partly by phosphoric acid.
Sat;sfactory particles were obtained.
As will be seen from the above Examples, the present
invention is capable of producing good quality microspheres
without ammonia emission, without a fusing step and in
small quantity although our experiments indicate that
large quantity production is also possible.
