Note: Descriptions are shown in the official language in which they were submitted.
~ ~3060~35
--1--
~e~
Raolinite Aggregation Using
Organo-Silicon Compounds
Field of the Invention
This application relates to the preparation of
chemically aggregated kaolinite using organo-silicon compounds.
The products are useful as fillers and coatings for paper.
S Background of the Invention
Kaolinite based pigments are commonly used in paper
industries for paper filling and paper coating applications. In
general, the objectives of using the pigment are to improve paper
qualities, such as opacity, brightness, smoothness, printing,
porosity, ~urface coverage, light scatter, and to reduce the cost
of paper manufacturing.
Both the brightness characteristics of the given kaolin
and the opacifying properties of same when incorporated as a
filler in paper, may be quantitatively related to a property of
the filler identified as the ~scattering coefficient S.~ The
said parameter, i.e., the scattering coefficient S of a given
filler pigment, is a property well-known and extensively utilized
in the paper technology art, and has been the subject of numerous
technical papers and the like. The early exposition of such
measurements was made by Xubelka and Munk, and is reported in
Z. Tech Physik 12:539 t1931~. Further citations to the appli-
cable measurement techniques and detailed definitions of the said
scattering coefficient are set forth at numerous places in the
patent and technical literature. Reference may usefully be had
.~
~3~6~S
--2--
in this connection, e.g., to U.S. patents Nos. 4,026,726 and
4,028,173. In addition to the citations set forth in these
patents, reference may further be had to Pulp and Paper Science
Technology Vol. 2 "Paper," Chapter 3, by H. C. Schwalbe (McGraw-
Hill Book Company, N.Y.).
In a filled paper, higher light scattering is therefore
important. Increased light scatter allows paper to look more
opaque without increasing light absorption. The use of pigment
with a higher light scattering coefficient allows reduction in
either the basis weight or amount of filler required to achieve
targeted properties, for example, opacity and brightness. Tradi-
tionally, this has been achieved using titanium dioxide, calcined
clays and precipitated calcium carbonate. The relatively higher
light scattering of titanium dioxide is due to higher refractive
index. Higher light scatter observed with calcined kaolin and
precipitated calcium carbonate is believed to be due to the
intrinsic porous structure developed during the process of manu-
facturing of these pigments. See McConnell et al, U.S. Patent
No. 4,381,948.
ln general, the attempt to increase light scatter by
modification of kaolinite mineral also induces some increase in
pore void volume. In addition, such modification can produce
pigments with particle siz~ distribution in a fairly narrow range.
For example, calcining of fine kaolinite above its dehydroxyla-
tion point can produce a product with increased pore void volume.
~3a~
--3--
In u.S. Patent No. 4,820,554 issued April 11, 1989 similar
aggregation is achieved chemically by reacting fine
kaolinite clay with rapidly hydrolyzing metal chlorides.
The acidic by-product of this reaction may be neutralized
with gaseous ammonia. The light scattering coefficient and
pore void volumes of these clays are significantly higher
than the starting kaolinite material. Marginal increase in
light scatter (generally less than 10 units) may be induced
by mixing kaolinite particles of dif~erent size or by
chemical flocculation. However, these structures are
generally unstable and would break down under high shear
stress of paper making or paper coating.
Aside from use as fillers, the aggregated
pigments are used in paper coating to improve surface
coverage. The application of such pigments can lead to a
smoother surface, higher porosity, gloss and print
properties. In the said patent application a chemically
aggregated kaolin pigment is shown to significantly
ircrease coated sheet properties, especially paper and
print gloss.
In more detail, in U.S. Patent No. 4,381,948 to
A. D. McConnell et al, a calcined kaolin pigment is
disclosed and a method for manufacture of same. The said
pigment consists of porous aggregates of kaolin platelets,
and exhibits exceptionally high light scatt~ring
characteristics when incorporated as a filler in paper.
This pigment, which substantially corresponds to the
- commercially available product ALPHATEX~ of the present
assignee, E.C.C. America Inc. (Atlanta, Georgia) is
prepared by ...
~3~ 5
first blunging and dispersing an appropriate crude kaolin to form
an aqueous dispersion of same. The blunged and dispersed aqueous
slurry is subjected to a particle size separation from which
there is recovered a slurry of the clay, which includes a very
fine particle size; e.g. substantially all particles can be
smaller than 1 micrometer E.S.D. The slurry is dried to produce
a relatively moisture-free clay, which i5 then thoroughly pul-
verized to break up agglomerates. This material is then used as
a feed to a calciner; such feed is calcined under carefully con-
trolled conditions to typical temperatures of at least 900 C.The resulting product is cooled and pulverized to provide a pig-
ment of the porous high light scattering aggregates of kaolin
platelets as described.
Calcined kaolin products, including those of the afore-
mentioned ALPHATEX type, are seen to be manufactured by rela-
tively complex techniques involving a multiplicity of steps,
including specifically a calcining step, plus various preparatory
steps and post-calcining steps. Thus, the said product is rela-
tively expensive to produce; and requires considerable investment
in complex apparatus and the like -- e.g. highly regulated cal-
ciners, etc. It can indeed be noted that the conditions of pre-
paration of these materials must be very careully controlled in
order to keep abrasion acceptably low in the calcined product.
For example! the calcination operation tends per se to produce an
abrasive product -- in consequence of overheating -- if great
care is not taken to preclude such a result.
: L3~6~
5--
It is further to be noted that in order to
produce a low abrasion calcined product, the particle size
in the feed to the calciner must be carefully controlled -
- even a relatively small increase in coarseness of such
feed can have very marked detrimental effect on Valley
abrasion.
In U.S. Patent 4,820,554 issued April 11, 1989,
a process is disclosed in which a fine particle size
kaoline is reacted in particulate form with a metal
chloride, such as silicon tetrachloride, to form a
chemically aggregated structured kaolin pigment. The
metal chloride may be one or more of the chlorides having
the general formula MClx, where M is Si, Ti or Al; and X is
3 or 4 depending on the valence of M. Heating may
optionally be used to shorten the reaction time. When so
used, temperatures generally will not, however, exceed
about 150C. In order to complete the polymerization and
condensation which is thought to occur, it is preferable to
age the resulting product for a period, typically at least
three days. In another aspect of that process, additional
improvements in the products are found to occur by the
addition of ammonia to the combined kaolin and metal
chloride.
Thus said patent application describes methods of
preparing chemically aggregated kaolinite mineral using
very reactive metal chlorides such as silicon tetrachloride
and titanium tetrachloride. The application of such
reactive metal chloride leads to aggregated products that
give enhanced optical and printability properties for both
filled and coated papers.
13~6~1~5
--6--
However, due to the nature of the aggregating chemical, very
specialized equipment and processing steps are required. In
addition, the resultant by-products are difficult to remove by
ordinary methods. In this invention, similar aggregates may be
S produced by reaction with organo-silicon compounds that are
non-corrosive and produce no so:Lid by-products~
It is known from U.S. patent 3,567,6~0 to Joseph
Iannicelli, assigned to J.M. Huber Corporation, issued March
2, 1971, that mercaptopropyl silanes having the formula:
~ORl
Z ' S X Si --OR2 ~1 )
OR3
wherein Z is selected from the group consisting of
hydrogen, cation, alkyl, aryl, alkylaryl, arylalkyl and deriva-
tives thereof; X is selected from the group consisting of alkyl,
alkylaryl, and arylalkyl; and Rl, R2 and R3 are selected from
the group consisting of hydrogen, cation and alkyl, are suitable
for moclifying kaolin clays to enable them to be used as rein-
forcing illers for elastomers. In fact the thus modified clays
have been the candidates of choice for such fillers in commerce.
It may be noted that in the Iannicelli disclosure, only the
trialkoxy mercaptopropyl silanes are considered. Blends of these
mercapto organosilanes with amino organosilanes are also dis-
closed.
In U.S. Patent No. 3,364,059 to Mar~occhi, a method
for treating glass fibers to improve their bonding relationship
~7- ~3~t~8~ -
to rubbers comprises treating them with a silane containing a
thio group.
According to the present invention, the thio group
and the amino group are not required. Sulfur-free and
nitrogen-free organic silicon compounds are employed.
In U.S. patent 3,834,92~1 to Thomas A. Grillo,
assigned to J.M. Huber Corporation, an amino organosilane is
added to a high solids content pigment dispersion or slurry to
change the slurry form into a thick, flocculated and plastic-
type that is suitable for extrusion and drying. Because athick, cake-like product is formed, the amino organosilane and
pigment dispersion are preferably mixed or blended directly in
a solids mixing apparatus such as an extruder, designed to
extrude the plastic mass in the form of a compacted rad type
body which may be fed directly into a drier. The products are
useful as a filler for polyurethanes. As can be seen, the
described treatment is for the different purpose of forming a
flocculated, plastic mass of the kaolin, not for the purpose
of aggregat.ng fine kaolin particles to form aggregated fine
kaolin particles.
In U.S. patent 3,894,882 to Robert B. Takewell et al,
assigned to J.M. Huber Corporation, a rotating pelletizing drum
is used to form pellets from clay sucn as kaolin clay. To
avoid the problem of dust, a wetting liquid is introduced into
the drum, preferably steam or steam~water. The steam adds heat
to the pellets to aid in drying them. There is an incidental
131~
mention of using "other suitable wetting liquids", an extensive
list being given which includes silanes.
In accordance with the foregoing, it may be regarded
as an object of the present invention to provide an aggregated
kaolin pigment product which possesses improved pigment bulk,
porosity and light scattering characteristics, and hence is
useful as a bulking pigment for coating of paper and paper
board, and which may also be used as an opacifier and light
scattering .iller for paper and paper board as well as in other
paper manufacturing applications.
It is also an object of the invention to provide a
pigment product of the foregoing character which is prepared
without calcination and therefore without subjecting the
kaolinite to high temperatures, and which accordingly possesses
low abrasiveness in accordance with the kaolinite feed from
which it is produced.
Another object of the present method is to demonstrate
application of substantially dry kaolin pigment in aggregation.
Yet another object is to demonstrate aggregation of
kaolinite particle by dry processing routes.
Yet another object is to demonstrate use of aggregated
pigment made by the present invention in paper filling to enhance
optical properties.
Yet another object is to show the application of such
pigment in light weight coatings.
-9- ~3~
Yet another object is to show the production of the
pigment in the presence of an aggregation enhancer such as
calcium chloride.
It is a further object of the present invention to
S produce pigment that is free of soluble salts.
It is yet another object of the present invention to
produce a pigment that, as a consequence of aggregation, can
be processed to a slurry at a solids content higher than 60
by weight without unduly poor rheological consequences.
It is yet another object of the present invention to
provide a process wherein aggregation efficiency, i.e. light
scatter, is improved by application of gaseous ammonia.
It is an object of the present invention to produce
aggregated kaolinite pigment with minimum steps in producing
lS said pigment.
It is also an object of the present invention to
produce aggregated kaolinite pigment at relatively low cost
compared with available such products.
Summary of the Invention
The present invention comprises a method of producing
aggregated kaolin pigments, specifically structured kaolin
pigments, using organo-silicon compounds either singly or in
combination. In general, the compounds may be selected from
the following:
-lo- ~3Q~085
Symmetric Compounds
OR
RO-Ii-OR
OR
R=CH3~ C2H5
C3H7, n-C4Hg,
sec-c4H9~ C6H5
Asymmetric Compounds
OR OR R
RO-Si-X Ro-Si-R RO-Si-R
OR OR OR
R=C2H5 X = Cl, Br R = H
In a typical process, substantially dry kaolin mineral is treated
with an effective amount of an organo-silicon compound such as
silanes having the formula (RO)4Si, where R is a lower alkyl
group of 1 to 4 carbon atoms, e.g., methyl (CH3), or ethyl
(CH3CH2). The R groups in the silane can be the same or differ-
ent. The resulting products exhibit increased light scatter,
improved wet void volume and bulk. The aggregates seem to have
a permanent structure that is strong enough to withstand the high
shear forces of paper making and paper coating.
Aggregation enhancing chemicals, which may optionally
be used, comprise alkaline earth metal chlorides and lithium
chloride. Amounts used of this aggregation enhancing agent may
be in the range of 0.05 to 3.0~, typically 0.05 to 2% by weight
of the salt based on the weight of the dry kaolin.
3~
Typically, feed moisture is in the range of 1 to 2~,
preferably 1.0 to 1.75% by weight of the feed clay. The most
preferred range is 1.5 to 1.75~ by weight of the clay.
The amount of organic silicon compound may range from
S 0.1 to 3.0%, preferably from 0.2 to 2.0~ by weight of dry kaolin.
Brief Description of the Drawings
In FIGURE 1 are compared the particle size distribu-
tion of the starting material and an aggregated product prepared
using 1~ tetramethoxysilane.
In FIGURE 2 are plotted the brightness of coated sheets
using aggregated pigments and a control consisting of fine clay
and calcium carbonate.
In FIGURE 3 are plotted the opacity of coated sheets
using aggregated pigments and a control consisting of fine clay
and calcium carbonate.
In FIGURE 4 are plotted the paper gloss of coated
sheets using aggregated pigments and a control consisting of
fine clay and calcium carbonateO
In FIGURE 5 are plotted the print gloss of coated
sheets using aggregated pigments and a control consisting of
fine clay and calcium carbonate.
In FIGURE 6 are plotted the litho print gloss of
coated sheets using aggregated pigments and a control consist-
ing of fine clay and calcium carbonate.
In FIGURE 7 is plotted the effect of feed clay
moisture on the light scattering characteristic of aggregated
-12- ~3~ 85
kaolinite prepared using 1% tetramethoxysilane.
In FIGURE 8 are plotted the percent wet void volume
of aggregated pigments vs. amounts of the aggregating agent.
In FIGURE 9 are plotted the light scatter of aggre-
gated pigment vs. amounts of aggregating agent.
In the ensuing description, all scattering data are
normalized by comparison to the scattering coefficient of
samples of the aforementioned Alphatex~. Ideally in a study
of the present nature, the same batch of beaten pulp should be
used throughout. As this is not practical, the method adopted
was to fill one set of sheets in each series of tests using the
same Alphatex~ from series to series. Statistically, the
Alphatex~ filled samples at 10~ filler had a scattering coeffi-
cient of 680 cm2/gram, and in each series in which Alphatex~
differed from 680, the scattering coefficients of the experi-
mental samples were accordingly adjusted proportionally to the
adjustments which the Alphatex~-containing paper required to
bring its value to 680 cm2/gram. This procedure, which was used
in subsequent examples, is from time to time referred to in the
specification as "normalizingN the scattering coefficients.
Detailed Descri~tion
General Methods of PreParation of Feed Cla~
This corresponds to preparation of the commercial
product Betagloss~ of the assignee E.C.C. America Inc. (Atlanta,
Georgia).
~10~8~
-13-
The starting crude material was a blend of crude kao-
lins, which were derived from northeast Georgia, and which were
comprised of very fine particle size materials. The GE bright-
ness of the said crude was in th~e range of 82 to 37. In all
instances in this specification it will be understood that
brightness values are obtained according to the standard specifi-
cation established by TAPPI procedure T-646 os-75.
The crude clays were beneficiated according to the gen-
eral practice used in kaolinite processing industries. The bene-
ficiated clays were classified by centrifugation to 94% less than2 micrometer E.S.D. (equivalent spherical diameter). The classi-
fied clays were flocculatsd using 0.25~ by weight of aluminum
sulfate and adjusting the pH to 3.5 with sulfuric acid. The
flocculated kaolinites were filtered. The significantly dried
(about 20% moisture remains) kaolinites were redispersed with
0.25~ by weight of sodium polyacrylate and the pH adjusted to
about 7Ø The redispersed kaolinite was spray dried.
This method of preparing fsed clays is general and
may be varied, particularly if so pointed out in specific
Examples; the main variations are differences in particle si~e
distribution and the addition of calcium carbonate.
Standard Method of Relative Sedimentation Volume Measurement
The relative sedimentation volume of treated and start-
ing material was measured to determine the exten~ and nature of
aggregation. In the procedure, a nearly 55% solids slurry of
pigment was prepared that contained 0.3 milliliter of sodium
31~
polyacrylate. This slurry was then spun at 7000 rpm for 45 min-
utes. The sediment volume was calculated using dry weight of
clay, wet weight of clay, and calculating volume of clay using
density of dry clay of 2.6g/ml.
The invention is demonstrated in the following examples
which are intended to be illustrative but not limitative.
Example 1
The starting feed clay was prepared from a blend of
two fine Northeastern crude clays from Georgia. The crude clays
were refined by common commercial beneficiation methods. The
refined clay was classified to 96~ less than 2 micrometer E.S.D.
The classified clay was blended with ground calcium carbonate
JS
(Carbital -90) at 3% weight of dry kaolinite. The blend was
spray dried and pulverized using a pulverizer manufactured by
Mikropul Corporation. This clay will be referred to as Feed
Clay-I.
75 9. of substantially dry powder, moisture 0.85~,
of Feed Clay-I was treated with 1% by weight of tetramethoxy-
silane, supplied by Petrarch Chemical Co., with vigorous mixing
in a Waring blender. Once the mixing of powder with liquid was
completed, the clay was allowed to mix for an additional
1.5 minutes. Excess silane and resultant methanol as a by-
product were removed by subjecting the clay to vacuum (nearly
30 torr). The above process with tetramethoxysilane was
repeated once and the final product was allowed to dry at
150C for fifteen minutes.
~n~
-15-
The particle size distributions of the starting Feed
Clay-I and the final product are illustrated in Fig. 1. The
particle size distribution indicates formation of a structured
aggregate with very narrow particle size distribution.
Handsheets were prepared using the above aggregated
clay from bleached sulfite pulp. The sheets were filled at
three filler loadings. The reflectivity of the handsheets was
measured and converted to light scatter according to a modified
Kabulka-Munk equation. The normalized light scatter of sheets
filled at 10% filler loading with this product was 578 cm2/g.
This is a gain of 60 scatter units from untreated Feed Clay-I.
The intraparticle porosity of the pigment, given as percent wet
void volume and determined by the relative sedimentation method
(RSV) was 57.3%. This is an increase of about 17 percentage
units from the feed clay. The increase in wet void volume
indicates the formation of aggregate structure and development
of the permanent porosity.
Example 2
The process and the chemical used were essentially
identical to Example 1, except that the feed was a fine
commercial clay, Betagloss. The particle size distribution
and moisture of this feed clay were 94% less than 2 micro-
meter, and 0.85% respectively. The normalized light scatter
of a sheet filled with the final aggregated product, at 10%
filler loading, was 562 cm2/g. Wet void volume of the product
determined by RSV was 56.4%, an increase of about 16~ percentage
units over the feed clay.
-16- ~3~6~8~ -
Example 3
The feed clay, aggreclating agent and the mixing process
were essentially identical to that of Example 2, except that the
clay was treated with 0.45~ by weight of ammonia gas following
each evacuation step. The normalized light scatter of a sheet
filled with this pigment, at 10% filler loading, was 550 cm2/g.
The wet void volume of the product, determined by RSV, was
56.7~. Wet void volume and scatter respectively are about 16
percentage units and 30 scatter units higher than the feed clay.
Example 4
In this example Feed Clay-II was prepared by mixing
3% ground calcium carbonate with previously spray dried and
pulverized ~etagloss followed by drying at 150C for 15
minutes. The moisture of this feed clay-II was 0.6~% by weight.
The aggregating chsmical and the treatment process were
essentially identical to Example 1. The normalized light
scatter of a sheet filled with this pigment at 10~ filler
loading was 585 cm2/g, which is an increase of about 65 units
over the ~eed clay. Wet void volume is about 16 percentage
units higher than the feed clay, thus 55.9~.
Example 5
~eed Clay-II was treated by the es~entially identical
method and chemicals described in Example 3. The normalized
light scatter o~ a sheet filled with this pigment at 10~ filler
loading was 5~ cm2/g. There was an about 16.1 percentage units
increase in wet void volume over the feed clay following the
chemical aggregation, thus 56.1~.
6~5
Exa_ple 6
The feed clay and the process of treatment were
essentially identical to the method described in Example 2,
except that the aggregating agent was an organo-silicon
compound containing ethoxy groups. (CH3CH2O)4Si. The normal-
ized light scatter of a sheet filled with this pigment at 10
filler loading was 547 cm2/g. The wet void volume of the
product by RSV was 54.1%. Upon chemical aggregation, wet void
volume and light scatter increased by about 14 percentage units
and 27 scatter units respectively over the feed clay.
Example 7
The feed clay, aggregating agent, and the treatment
process all were essentially identical to the method described
in Example 6 except that the clay was exposed to 0.4S~ by weight
of ammonia immediately following the evacuation step as described~
in Example 3. The normalized light scatter o a sheet filled
with this pigment at 10% filler loading was 544 cm?/g. The wet
void volume determined by RSV of the product was 54.9%.
Example 8
The feed clay and process were essentially identical
to the method described in Example 4 except that the aggre~
gating chemical was tetraethoxysilane, (C~3CH2O)4Si. The normal-
ized light scatter of a sheet filled with this pigment at 10~
filler loading was 570 cm2/g. The relative sedimentation method
showed the product to have 52.1 percent wet void volume. The
increases in llght scatter and wet void volume amount to 50
: ~ ~
~3~ 85
-18-
scatter units and about 12 percentage units over the feed clay,
respectively.
Exc~m~le 9
The process and aggregating chemical were essentially
S identical to the method described in Example 7 except that Feed
Clay-II was the starting material. The normalized light scatter
of a sheet filled with this structured aggregated clay, at 10%
filler loading, was 584 cm2/g. In addition, the wet void
volume determined by RSV was 54.4~, an increase of about
14 percentage units over the feed clay.
Example 10
The process, aggregating chemical and the feed clay
all were essentially identical to the method described in
Example 1, except that the moisture content of the feed clay
was such that the molar ratio of water to silane was 9.69, which
is equivalent to a moisture content of the feed clay of about
1.11~ by weight. The relative sedimentation method showed the
product to have 57.5 percent wet void volume.
This product was used to determine coated sheet
properties of light weight coated offset grade paper. In the
coating formulationj 30 parts of regular coating pigment were
replaced with this product. The typical formulation and rele-
vant formulation properties are provided in Table 1.
Almost all of the coated sheet properties improved by
application of this aggregated clay, for example, sheet gloss,
print gloss and opacity. These coated sheet properties are
~1 30~Z 35
.
illustrated in Figures 2 through 6. The properties, i.e.
brightness, opacity, gloss, print gloss, and litho print gloss
are compared with a common offset control formulation.
Exan!ple 11
The feed clay and the process were essentially
identical to the method described in Example 10, except that
the aggregating chemical was (CH3C~2O)4Si, tetraetho~ysilane.
The relative sedimentation method showed the product to have
51.9 percent wet void volume, an improvement of nearly 12
percentage units over untreated feed clay.
As in Example 10, this pigment was evaluated in a
paper coating application. Once again, significent improvement
of coated sheet properties is observed with this aggregated
structure pigment. The essential coated sheet properties, e.g.
brightness, opacity, gloss, print gloss, and litho print gloss
are illustrated in Figures 2 to 6.
Example 12
It is postulated that the hydrolysis, and subsequent
polymerization of the hydrolyzed products, of the orsano-silicon
compound, e.g. silane, would depend on the availability of free
moisture. In the presence of excessive moisture it might be
possible that the hydrolyzed product would precipitate as an
amorphous silica. In this example, the effect of starting feed
clay moisture on aggregation is examined. The feed clay,
aggregating chemical and process all were identical to that of
Example 1, except that the moisture of the feed clay was varied
~L3~ 85
-20-
in the range of l to 2% by weight, so that the effective ratios
of total water to the amount of silane were in the range of
4.56 to 8.44. The light scatter values of the handsheets
prepared using respective aggreS~ated clays, at 10% filler
loading, are provided in Table 2. This relationship between
moisture and light scatter is graphically illustrated in
Figure 7. The effective aggregation can be achieved even at a
water to si]ane ratio of 8.44. The preferred range of moisture
appears to be between l.0 to 1.75~ by weight of dry clay.
Example 13
The feed clay, aggregating chemical and part of the
processing were identical to Example 12, the moisture of the
feed clay being 1.08% by weight, except that in the process
there was a time delay of lO minutes prior to the repeat
lS chemical treatment. The light scatter of a sheet filled with
this product at 10% filler loading was 582 cm2/g. Apparently
higher residence time is beneficial for developing a more
effectively structured aggregate.
Example 14
The starting material was a Feed Clay-I that contained
3% ground calcium carbonate, Carbital-90. The moisture of the
feed clay was adjusted to 3.29% by weight. 75 grams o this
feed clay was treated with l~ by weight of tetraethoxysilane,
(CH3CH2O)4Si, by the usual method of mixing, using a commercial
Waring blender. After addition of the silane, mixing was
continued for 1.5 minutes. The clay was then subjected to
~3~6~85
-21-
vacuum for about two minutes and the whole process was
repeated once. The final product was dried at 150C for 15
minutes. The wet void volume of the final product, as
determined by RSV method, was 51.2%, an increase of about 11
percentage units over the starting feed clay.
Example 15
In this example, moisture of the Feed Clay~I was
adjusted to 2.94% by weight and the clay was treated with 0.5~
by weight of tctraethoxysilane, (CH3CH2o)4si. The rest of the
treatment process was identical to that of Example 14. Wet
; void volume of this product was 46.2%, about 6 percentage units
higher than the feed clay.
Example 16
The feed clay, feed clay moisture, aggregating chemical
and the treatment process all were identical to those described
in Example 15, except that the amount of the aggregating agent
was 0.25% by weight of the clay. The wet void volume of this
product was 47.1%, an increase of about 7 percentage units over
the feed clay.
Example 17
This example demonstrates the reIation between the
amount of aggregating agent vs. aggregate performance by keep-
ing all other conditions the same. The starting material was a
Feed Clay-I in which the moisture was adjusted to 0.95% by
weight. This feed clay was treated separately using 0.25%,
0.5% and 1.0% by weight of tetraethoxysilane, tCH3CH20)4Si,
-22- ~3Q6~
according to the process described in Example 14. The normal-
ized light scatter of a sheet filled with these pigments at
10~ f iller loadings and percent wet void volumes of these
aggregated fillers are provided in Table 3. Also, the relation
between the amount of aggregating agents vs. wet void volume
and Light scatter of filled sheets are illustrated in Figures 8
and 9 respectively. It is evident that the silane enhances
these properties.
Example 18
This example further demonstrates the relation between
the amount of aggregating agent vs. aggregate performance by
keeping all other conditions the same. The starting material
was a Feed Clay-I where the moisture was adjusted close to
1.72% by weight. This ieed clay was treated separately using
0.25% and 0.5% by weight of tetraethoxysilane, (CH3CH20)4Si
according to the process described in Example 17. The normal-
ized light scatter of a sheet filled with these pigments at
10~ filler loadings and percent wet void volumes of these
aggregated fillers are provided in Table 4.
~ Example 19
This example describes use of an aggregation enhancing
agent, calcium chloride. In the process, Feed Clay-I was mixed
with 0.5% by weight of dihydrated calcium chloride salt and the
feed moisture was adjusted to 1.64~ by weight of the clay. The
chemical treatment process was identical to that of Example 17.
1.0% by weight of tetraethoxysilane was used. The normalized
-23- ~3~
light scatter of a sheet filled with this pigment at 10% filler
loading was 577 cm2/g. The resulting product is more porous as
indicated by the substantially higher wet void volume, 61.6%
measured by RSV technique.
Example 20
In this example, the effect of amount of aggregation
enhancing agent is examined. The feed clay and the chemical
treatment were identical to those described in Example 19,
except that in a first set, feed clay was separately dosed with
0.2, 0.5 and 1.0~ by weight of calcium chloride. In each case
moisture of the feed clay was adjusted to nearly 1.3~ by weight,
after mixing Feed Clay-I with calcium chloride. Similarly,
in a second set, feed clay was separately dosed with 0.05 and
0.1% by weight of calcium chloride except that the moisture
of the feed clay was adjusted to 1.9% by weight. Each of these
clays was treated with 0.5~ by weight of tetraethoxysilane.
The final products are porous aggregates as seen from wet void
volume, measured by RSV technique. The wet void volumes are
provided in Table 5.
Example 21
Previous examples have demonstrated that the use of
tetramethoxysilane produced more efficient aggregates; however,
tetraethoxysilane is more cost effective. Thus, ~o produce
efficient, but cost effective aggregates, a combination of
tetraethoxy- and tetramethoxy- silane was used in this example.
-24- 13~
The feed clay was identical to the one described in Example 14.
The moisture of the feed clay was adjusted to 0.85~ by weight.
The chemical treatment process was essentially identical to the
method described in Example 14 except that the composition of
the aggregating agents consisted of 0.25~ by weight of tetraet-
hoxysilane and 0.05% by weight tetramethoxysilane. The wet void
volume of the final product, determined by RSV techniquP, was
51.4%. This is an increase of nearly 11 percentage units over
the feed clay. The overall amount of chemical required is sig-
nificantly lower than that required for similar aggregation
using either tetraethoxy- or tetramethoxy- silane alone.
Example 22
The starting material for this experiment was a
commercial coating clay Betagloss. This clay, after initial
beneficiation, size cIassification, filtration and redisper-
sion was diluted to 40% by weight slurry. This slurry was
spray dried and pulverized using a pulverizer produced by
Mikropul Corporation. The particle size distribution of this
clay was 94% less than 2 micrometer E.S.D. The moisture of
this clay was adjusted to 0.86% by weight. 75g. of this clay
was treated with 0.25~ by weight of tetraethoxysilane,
(CH3CH2O)4Si, using a commercial mixer, a Waring blender. The
wet void volume determined by relative sedimentation method
- was 57.3~. This is a substantial increase over feed clay wet
void volume of 40~.
~3016~5
-25-
Example 23
The feed clay, treatm~nt process, aggregating chemical
and amount of the tetraethoxysilane were identical to that in
Example 22 except that the feed clay was dosed with 0.13 by
weight of an aggregation enhancing chemical, calcium chloride,
and the moisture of the feed was adjusted to 0.98~ by weight.
The percent wet void volume of the product was S0.4%, an in-
crease of about 10 percentage units over the feed clay.
Example 24
Feed Clay-I was equilibrated with moist air to
increase moisture of the feed clay from 0.85~ to l.S~ by
weight of the clay. This clay was treated with O.S~ by
weight of tetraethoxysilane, (CR3CH2o~4si~ under vigorous
mixing conditions using a commercial mixer, a Waring blender.
After the treatment with tetraethoxysilane, mixing was con-
tinued for an additional l.S minutes. This product was dried
at 150C for 15 minutes. Wet void volume of this product was
50.5~ by weight.
Example 25
The feed clay and chemical were identical to that
described in Example 24. This time the feed clay was mixed
-with 0.5~ by weigh of an aggregation enhancing agent, calcium
chloride and the molsture of the feed clay was adjusted to 1.8
by weight of the cIay. 75g. of this clay was treated with 0.5%
by weight of tetraethoxysilane, (CH3C~2O)4Si, in a Waring
blender. After the addition of the silane, mixing was continued
13~ 8~ .
-26-
for 1.5 minutes. The clay was then subjected to vacuum for
about two minutes. The above process with tetraethoxysilane was
repeated once. The final product was dried at 150C or 15
minutes. The wet void volume of the final product was 50.1%,
about 10 percentage units higher than the feed clay.
Exarnple 26
A series of experiments was conducted using Feed
Clay-I as a starting material. The moisture of the feed
clay was adjusted to 1.0% by weight. Three separate portions,
75g each, were treated with 0.25% by weight of tetraethoxy-
silane, (CH3CH2O)4Si, according to Example 13, except that the
time between each chemical treatment was increased to 15, 30
and 60 minutes. The normalized light scatter of handsheets
filled with these pigmen~s at 10% loadings is given in Table 6.
In addition, the particle porosity measured as wet void volume
is included in Table 6. In each case the light scatter and
wet void volume improved significantly from the starting
material.
-27- ~3~6~B~
Table 1
Formulations and Coating
Formulation Properties
_________________________________________________ __ ________
Formulation Control Pigment A* Pigment B**
Components 30 parts 30 parts
___________________________________________________ _________
~1 Clay 75 parts 60 parts 60 parts
Calcium 2S parts 10 parts 10 parts
Carbonate
Latex 10 parts 10 parts 10 parts
Starch 4 parts 4 parts 4 parts
Nopcote C-104 0.5 part O.S part 0.5 part
Sunrez 700 M 3.12 part 0.12 part 0.12 part
Dispex N-40 0.1 part 0.1 part 0.1 part
pH 7.6 8.0 8.1
% Solids 64.1 63.9 63.8
Brookfield
Viscosity
100 rpm (cps) 880 1080 1040
_____ ____________ _______________________________ _____ _
: *Prepared by using Tetramethoxysilane
**Prepared by using Tetraethoxysilane
J~
-28- 13~
Table 2
Effect of Feed Clay Moisture on
Light Scatter of Handsheets Filled ~Jith
- 10~ Chemically Aggregated Kaolinite Pigment
______________________________________________________________
Percent Water/Silane Normalized Light
Moisture Moles/Moles Scatter at 10~
Filler Loading
______________________________________________________________
2.0 8.44 563
1.71 7.22 574
10 1.08 4.56 574
____________~_____~___________________________________________
Table 3
Effect of Silane Concentration on the
Properties of Aggregated Kaolinites
Prepared Using Tetraethoxysilane
____________________ ____ ________________ ________________ ,
Percent Molar Ratio Normalized Percent
Chemical of Water to Light Scatter ~et Void
Silane at 10~ Filler Volume
Loading
___________________ ____________ ____________ _____________
0.25 21.96 549 47.7
0.5 10.98 551 49.3
l.0 5.48 563 S0.0
_____ __ ____________________ ____ ________________________
-29- ~3~D6~
Table 4
Effect of SiIane Concentration on the
Properties of Aggregated Raolinites
Prepared _sing Tetraethoxysilane
~: -- -- ______________. ________
~ 5 Percent Molar Ratio Normalized P~rcent
: Chemical of ~ater to Light Scatter Wet Void
Silane at 10~ Filler Volume
Loading
_______ _________
0.25 39.76 562 ~8.9
0.5 20.10 56~ 50.2
--____________
Table 5
Effect of Calcium Chloride on ~et Void
Volu~e of Chemically Aggregated Raolinites
Amount of Feed Clay Percent Wet
Calcium Chloride Moisture Void Volume*
(% by weight) (% by weight)
______._______________________________________ ____._________ .
0.05 1.9 51.1
0,1 1.9 51.1
0.2 1.3 53.0
0.5 . 1.3 62.5
1.0 1.3 62.9
_____________ ____ ___________________________________________
*The wet void volume of the feed clay was ~0.2.
-30- ~3~
Table 6
. _ _
Effect of Time Delay ~etween Chemical
Treatment Steps in the Aggregation of
Kaolinlte Usinq 0.?5~ Tetrametho~ysilane.
_____________________________________________________________
Delay Time Normali~ed Light Percent WQt
- (Minutes) Scatter at 10~ Void Volume
Filler Loading
________ ____________________ _ _____________________________
542 52.2
546 55.6
544 52.0
______________________________________________________________
When used in paper coating applications, the structured
kaolin pigments of the invention comp~ise from about 5 to 60~ and
preferably from about 10 to 30% by weight of the total pigment
component of the coating composition. The balance of the pigment
can comprise any of the known coating pigments, such as coating
grades o~ kaolins, calcium carbonate, titanium dioxide, plastic
pigments, etc. The coating ccmpositions, in addition to the pig-
ment component, include conventional components, such as an adhe-
sive binder, dispersants, and other known additives.
While this invention has been particularly set forth
in terms of specifics, it is understood in view of this disclo-
sure, that numerous variations upon the invention are now enabled
to those skilled in the art, which variations yet reside within
the scope of the present teaching. Accordingly, the invention is
to be broadly construed, and limited only by the scope and spirit
of the claims now appended hereto.
