COATING COMPOSITION AND COATED PAPERAND COATED PAPERBOARD

(19) United States
(12) Patent Application Publication (10) Pub. No.: US2014/0370273 A1
Lyons et al.
US 20140370273A1
(43) Pub. Date: Dec. 18, 2014
(54)
(71)
(72)
(73)
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(22)
(86)
(60)
COATING COMPOSITION AND COATED
PAPER AND COATED PAPERBOARD
Applicant: IMERYS PIGMENTS, INC.,
ROSWELL, GA (US)
Inventors: Anthony Lyons, Macon, GA (US);
Chinmay Peshave, Milledgeville, GA
(US)
Assignee: Imerys Pigments, Inc., Roswell, GA
(US)
Appl. No.: 14/370,285
PCT Fled: Oct. 10, 2013
PCT NO.: PCT/US13A64293
S371 (c)(1),
(2), (4) Date: Jul. 2, 2014
Related U.S. Application Data
Provisional application No. 61/715,628, filed on Oct.
18, 2012, provisional application No. 61/787.222,
filed on Mar. 15, 2013.
Publication Classification
(51) Int. Cl.
C09D I/00 (2006.01)
C09D II/32 (2006.01)
C09D 13.3/08 (2006.01)
(52) U.S. Cl.
CPC ................ C09D I/00 (2013.01); C09D 133/08
(2013.01); C09D 101/32 (2013.01)
USPC ... 428/330; 106/286.5; 524/425: 106/170.57
(57) ABSTRACT
A coating composition may include kaolin having a shape
factorless than about 70andcalciumcarbonate, whereinless
than about 90% by weight and greater than about 60% by
weight ofparticles ofthe calcium carbonate havean equiva
lentspherical diameter(esd) less than2 microns.The coating
composition may include a thickener present in an amount
ranging from about 0.1% to about 0.9% by active dry weight
of the composition. A coating composition may include
kaolin having a shape factor less than about 70 and calcium
carbonate having a mean particle size (ds) ofat least about
2.4 microns and a steepness factor ofat least about 30. The
coatingcomposition may beapaperbasecoat composition or
a paperboard basecoat composition. A paper or paperboard
product may include the coating composition on at least one
Surface ofthe paper product orpaperboard product.
dmax
dmax= PL/48 El

Patent Application Publication Dec. 18, 2014 Sheet 1 of 11 US 2014/0370273 A1
-
- dmax
A
~x.
Ömax= PL/48 El
Fig. 1
{
WWWMWM-nm-Mmm-mm-mm-mm-vumumum-Mammammammam
--5
C W-----WW- W----------------------------------------------- - -W--------------- - -W- ---------------------
2 2A A
Clay:Carbonate 50:50 Blends *PWAc 1103 latex: 20
Fig. 2

Elastic Modulus of Coated Paper Board:
Top Coatwith CGCC4 plus CKS3 and Base Coat combinations
BC1 EC2 EC3 B4 BCS EC6
Base Coats
Top Coat used:- CGCC4: CKS330:70 (latex20parts)
FIG. 3
Stiffnessof Coated Paper Boards
Top Coat withCGC4 plusCKS3 and ease Coatcarbinations
BC EC2 B3 BCA BC, C
Base Coats
Top Coat used: CGCC4: CKS330:70 (Latex 20parts)
FIG. 4

PatentApplication Publication Dec. 18, 2014 Sheet 3 of 11 US 2014/0370273 A1
Elastic Modulus of Coated Paper Boards
--r with Base Cat:4.
Top Coats
- with Base Coatia
0.020 -
Stiffnessof Coated Paper Boards
0.015 -
0.010
0.000 --------------.pooroooooo-error-in-ron-roooo-o-ongo-o-ooooo-oo-oorooooo-oo-oor
TC C3
Top Coats
FIG. 6
with Base Citi2
” with B.S. Ct.
Ca

Flakingand Cracking Results vs Thickener Levels
0 Flaking
Cracking
BendingStiffness ResultsvsThickener levels
O.3 0.4 O5 O. .. O.8 O.9
Thickener Levels (pph)

Flaking Ratings vs Base Coat Weight
11.5 12 2.5 3. 13.5 14 14.5 5
BaseCoatWeightgsm)
FIG. 11
Cracking Ratings vs Base Coat Weight
: 1. 2 2.5

Flaking Ratings and Bending Modulus Results
Normalizedwith CoatWeighty
1
now- www.wam. -o-as- away----- M w-r- : ro- O.)
CGCCfCKS2 CGCC1/CKS2 GCC1/CKS2 CGCC KSI GCC1/KS1 GCC1ACKS2 CGCCLfoRS1 CGCC1/CRS1
PA 32 135 A 3 &
Coating Formulations lessamentinedseparately,the inderused
is-PA103 BASFP3.08:1--1a:22parts
FIG. 13
CrackingRatings and Bending Modulus Results
Nolinalizedwith CoatWeightvariations
10 -----------------------
H- mm-mm-mm-mm-W 5
O
5.
s
CGCC folkS2 CGCC cKS2 GCC for82 CGCC. KSI GCC) frkSI GCC ifCKS2
W 32 W. 38 32
3.
less meationed separately, thebinder
set is-AgaSF 38:
1.3-lit-22arts
CoatingFormulations
FIG. 14

Flaking Ratingsand Bending Stiffness Results
Normalizedwith CoatWeightW:
V------a m- a--sman v m -, -, a KX
v-- www. KX - v-was----- ------------------ - v
CGCC KS1 GCC1/CKS2 CGCCLACKS. CGCC1/CKS (CCACKS2
Ac3 A FAC 13
22 2 6
CoatingFormulations unlessmentionedseparately,thebinderused
is-WAct 103+BASF P3.08:14-11-22parts
FIG. 15
CrackingRatings and Bending Stiffness Results
NormalizedwithCoatWeight Wariations
O32
:
024
.
: - --------.p.----------- -- 22
GCC1 folkS2 GCCF KS CGCC1/CKS2 CGCC1/KS GCC CKS. CGCC1ficks CGCC CKS GCC1folkS2
Fiat (3 PA 3 FA 3
2
Coating Formulations Jess rentioned separately, thebinier used
is-PVAC103-EASF308;11 +1=22parts
FIG. 16

BendingStiffness Results Normalizedwith Base & Top CtWt
ME) CD Geo. Meal
O.022 -------
5 0.020 ---
. O.08 - ------------W-m-W-m--A-ry--
A A WN A
0.016 --- { 00%
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
0.014 50/50 Ratio
0.012 -- A 25/75 Ratio
{
| g 0.010 - -
0.008 serveneerworror-o-o-o-o: - all-wa-la-nui-a-
2 g- s' s” s s g: g: s s
a.
| s : g g s
Bulk Comparison ofPlaty Clay:Carbonate Blends
0CKS2/GCC2
KS2/GCC2
s ACKS1/GCC2
r
OKSI/GCC2
i * CKS2/CGCC1
KS2/CGCC1
CKS1/CGCC1
A KS1/CGCC1
100% CGCC1
OO
Percent Carbonate Biggerallets of biei is is gearstar a bonate 3CC2

Mercury Porosimetry Results; Total intruded Pore Volume
-- -
G.5O
O.t 5 8. --- -- ------ --
O, O
0.30 . . .
CGCC SC (KSACGC CKSfSC KS2/CGC k$2.3CC2 KSA GC KSfc.co.2
100% 100% se:St. Se:S St:50 50:50 SOS 50:50
Base Coats
T ialSamples top coatplusBasecoat.Top coatisconstant:cKS3/cgc.ca 30:70
www.kewa -xx-assassrs ... mosa-3-w x-awww.r-view
FIG. 20

US 2014/0370273 A1
COATING COMPOSITION AND COATED
PAPER AND COATED PAPERBOARD
CLAIM OF PRIORITY
0001. This PCT International Application claims theben
efit ofpriority ofU.S. Provisional Application Nos. 61/787,
222, filedMar. 15,2013, and 61/715,628, filedOct. 18, 2012,
the subject matterofboth ofwhich is incorporated herein by
reference in their entireties.
FIELD OF THE DISCLOSURE
0002 The present disclosure relates to coating composi
tions, and more particularly, to coating compositions for
paperand paperboard products.
BACKGROUND OF THE DISCLOSURE
0003 Coatings may be applied on substrates to enhance
the physical and optical properties of the substrate. For
example, paper and paperboards used in the printing and
converting industries may be subjectedto a variety ofopera
tions, such as, for example, printing, cutting, creasing, fold
ing,and/orgluing. Coatedpaperboardsarewidelyusedin the
packaging industry, and a typical coating formulation may
include one or more pigments, binders, and additives. Such
coatings may serve to enhance physical, optical, and/or bar
rierproperties ofthe products. Physical and/oroptical prop
erties mayprovideaestheticappealand/orfunctionalbenefits
to packaging formed from the coated substrates. Paper and
paperboard products may be very sensitive to moisture and
moisture vapors,andbarrierproperties may providea barrier
against moisture, oil, water vapors, or gases.
0004 Creasing and folding operations are important pro
cesses intheconvertingindustry. However, creasingandfold
ing may result in applying significant strains to the paper or
paperboardSubstrates. Such strainschallengethe mechanical
strength ofthe Substratesas wellasany coatinglayerspresent
on the Substrates. For example, rupture occurring at creased
and folded edges ofthe paperand paperboard products may
weaken barrier properties ofthe Substrate significantly and
may diminish the overall aesthetic appeal of a packaging
formed by the substrate.An inability to withstandthese large
strains mayleadtoruptureoffoldededges,potentially result
ing in large cracks orflaking-offofthe coating layer orboth.
0005 Traditionally, coating layers with higher stiffness
havebeenpreferred,sincehigherstiffness coatinglayers may
provide Superior strength and/or reduction in the fiber usage
forthe substrate. However, stiffercoating layers may tend to
increasetheseverity ofcrackingorflakingoccurringatfolded
edges ofpaper orpaperboards.
0006. Therefore, it may be desirable to provide coating
compositions that exhibit improved resistance to cracking
and/or flaking when the Substrates coated with the coating
composition are folded, or improved performance when the
Substrates undergo printing or converting operations.
SUMMARY
0007. In accordance with a first aspect, a coating compo
sition may include kaolin having a shape factor less than
about70andcalcium carbonate, whereinless thanabout90%
by weight and greaterthan about 60% by weight ofparticles
ofthe calcium carbonate have an equivalent spherical diam
eter (esd) less than 2 microns.
Dec. 18, 2014
0008. As used herein, “shape factor” is a measure ofan
average value (ona weightaveragebasis) ofthe ratioofmean
particle diameter to particle thickness for a population of
particles of varying size and shape, as measured using the
electricalconductivity methodandapparatusdescribedin,for
example, U.S. Pat. No. 5,128,606, and using the equations
derived in its specification. “Mean particle diameter' is
definedasthe diameterofacircle,whichhasthesameareaas
the largest face ofthe particle. The electrical conductivity of
a fully dispersed aqueous Suspension ofthe particles under
test is caused to flow through an elongated tube. Measure
ments ofthe electrical conductivity are taken between (a) a
pair ofelectrodes separated from one another along the lon
gitudinal axis ofthe tube, and (b) a pair ofelectrodes sepa
ratedfrom oneanotheracrossthetransversewidth ofthetube.
Using the difference between the two conductivity measure
ments, the shape factor ofthe particulate material undertest
may be determined.
0009. “Particle size.” as used herein, for example, in the
contextofparticlesizedistribution (psd), maybe measuredin
terms of equivalent spherical diameter (esd). Sometimes
referred to as the “ds value, mean particle size and other
particle size properties referred to in the present disclosure
may be measured in a well-known manner, for example, by
sedimentation oftheparticulate material in a fully-dispersed
condition in an aqueous medium using a SEDIGRAPH
5100TM machine, as supplied by Micromeritics Corporation.
Such a machine may provide measurements and a plot ofthe
cumulative percentage by Weight ofparticles having a size,
referredto in theartas “equivalentspherical diameter” (esd),
lessthanthegiven esd values. Forexample,the mean particle
sizedo is the valuethat maybedeterminedin this way ofthe
particleesdat which thereare 50% by weightoftheparticles
thathave an esd less than that do value.
0010. According to another aspect, the coating composi
tion may includeathickener. Forexample,thethickenermay
be present in an amount ranging from about 0.1% to about
0.9% by active dry weight ofthe composition, in an amount
ranging from about 0.2% to about 0.6% by active dry weight
ofthecomposition, in anamount ranging from about 0.4% to
about 0.9% by active dry weightofthe composition, or in an
amountrangingfrom about0.4% to about0.6%by active dry
weight ofthe composition. According to a furtheraspect, the
thickenermaybeselectedfromthegroup consistingofalkali
soluble emulsion polyacrylate thickeners, hydrophobically
modified alkali-soluble emulsion polyacrylate thickeners,
and CMC (carboxymethyl celluloses) thickeners.
0011. According to still another aspect, less than about
30% by weight ofthe kaolin has an esd less than about 0.25
micron. For example, less than about 25% by weight ofthe
kaolin has an esd less than about 0.25 micron, or less than
about 20% by weightofthe kaolin has an esd less than about
0.25 micron.
0012. According to yet another aspect, the kaolin has a
mean particle size (do) less than about 1 micron. According
to anotheraspect,less thanabout80%byweightofthe kaolin
has an esd less than about 1 micron. According to a further
aspect, less thanabout90% byweightofthekaolinhasanesd
less than about 2 microns.
0013. According to still a further aspect, less than about
80% by weightand greater than about 60% by weight ofthe
particles of the calcium carbonate have an esd less than 2
microns. For example, less than about 70% by weight and

US 2014/0370273 A1
greaterthan about 60% by weightofthe particles ofcalcium
carbonate have an esd less than 2 microns.
0014. According to yet another aspect, the coating com
position is a paper basecoat composition or a paperboard
basecoat composition. According to still a further aspect, a
paper product or paperboard product may include a coating
composition on at least one Surface ofthe paper product or
paperboard product, wherein the coating composition
includes kaolin having a shape factor less than about 70 and
calcium carbonate, wherein less than about 90% by weight
and greater than about 60% by weight of particles of the
calcium carbonate have an equivalent spherical diameter
(esd) less than 2 microns.
0.015. In accordance with another aspect, a coating com
position may include kaolin having a shape factor less than
about70,andcalcium carbonatehavingadso ofatleastabout
2.4 microns and a steepness factorofat least about 30.
0016 Particle size distribution (psd) ofparticulate mate
rial can also be characterized by a “steepness' or“steepness
factor.”Thesteepness factorisderivedfrom theslopeofapsd
curve, where the particle diameter is plotted on the x-axis
against a cumulative mass percentage of particles on the
y-axis. A wide particle distribution has a relatively lower
steepness factor, whereas a narrow particle size distribution
gives rise to a relatively higher steepness factor. In some
aspects, the steepness factor may be calculated as a ratio of:
steepness = 30 x 100
d70
i.e., the ratio ofthe particle size at a cumulative mass ofless
than30% oftheparticles (do), totheparticle sizeata cumu
lative mass ofless than 70% ofthe particles (dzo), as deter
minedbyaSedigraph 5100,multipliedby 100.Asthedo and
do valuesapproach eachother,thesteepnessfactorincreases.
0017. According to yet another aspect, the mean particle
size (ds)ofthe calcium carbonatemay begreaterthanabout
2.6 microns, greater than about 2.8 microns, or greater than
about 3.0 microns. According to a further aspect, the steep
ness factor(e.g., do/dox100) ofthe calcium carbonate may
be greaterthan about 32, greaterthan about 34, greaterthan
about 36, greater than about 40, or greater than about 43.
0018. Itis tobeunderstoodthatboththeforegoinggeneral
description and the following detailed description are exem
plaryandexplanatory onlyandarenotrestrictiveoftheinven
tion.
0019. The accompanying drawings, which are incorpo
rated in and constitute a part of this specification, serve to
explain at least some principles ofthe invention.
BRIEF DESCRIPTION OF THE DRAWINGS
0020 FIG. 1 is a schematic representation ofa beam Sup
ported at its ends;
0021 FIG.2isagraphshowingelastic modulusofcoating
samples:
0022 FIG.3 is a graph showingelastic modulus ofcoated
paperboard samples;
0023 FIG. 4 is a graph showing bending stiffness of
coated paperboard samples;
0024 FIG.5 is a graph showingelastic modulus ofcoated
paperboard samples;
Dec. 18, 2014
0025 FIG. 6 is a graph showing bending stiffness of
coated paperboard samples;
0026 FIG. 7 is a graph showing flaking ratings ofcoated
paperboard samples;
0027 FIG.8 isagraph showingcracking ratings ofcoated
paperboard samples;
0028 FIG. 9 is a graph showing flaking and cracking
ratings vs. thickener levels;
0029 FIG. 10 is a graph showing bending stiffness vs.
thickener levels;
0030 FIG. 11 is a graph showing flaking ratings vs. base
coat weight;
0031 FIG. 12 is agraphshowingcrackingratings vs. base
coat weight;
0032 FIG. 13 isagraph showingflakingratingsandbend
ing modulus results for coating composition samples:
0033 FIG. 14 is a graph showing cracking ratings and
bending modulus results for coating composition samples:
0034 FIG. 15 isagraph showingflakingratingsandbend
ing stiffness results forcoating composition samples;
0035 FIG. 16 is a graph showing cracking ratings and
bending stiffness results for coating composition samples:
0036 FIG. 17 isa graph showing folding performance vs.
roughness results for coating composition samples;
0037 FIG. 18 is a graph showingbendingstiffness results
for coating composition samples;
0038 FIG. 19 is agraph showingbulk vs.compositionfor
coating composition samples; and
0039 FIG.20 isaisagraphshowingmercuryporosimetry
for coating composition samples.
DESCRIPTION OF EXEMPLARY
EMBODIMENTS
0040. Reference will now be made in detail to exemplary
embodiments ofthe invention.
0041 Applicant has surprisingly determined that flaking
and/orcrackingsometimes associated with the fold ofcoated
paperproductsandpaperboardproducts maybereduced by a
coating composition including a combination ofkaolin and
calcium carbonate. For example, a coating composition
including kaolin having a shape factor ofless than about 70
and calcium carbonate, wherein less than about 90% by
weight and greaterthan about 60% by weight ofparticles of
the calcium carbonate have an esd less than 2 microns, may
result in reduced flaking and/or cracking at a fold ofa paper
product or paperboard product coated with the coating com
position.
0042. According to some embodiments, the coating com
position may include a thickener, for example, a thickener
presentinan amount ranging from about0.1% to about0.9%
by active dry weight ofthe composition. For example, the
thickener may be selected from at leastone ofalkali-soluble
emulsion polyacrylatethickeners,hydrophobically-modified
alkali-soluble emulsion polyacrylate thickeners, and CMC
(carboxymethyl celluloses) thickeners.
0043. Notwishingtobeboundby theory,itisbelievedthat
the packing structure of the coating layer provided by the
coatingcompositionaccordingtoatleastsomeembodiments
disclosed herein may result in improved modulus and stiff
ness ofthe coating,as wellas improved (i.e.,reduced)flaking
and/orcracking ofthe coatingat the fold ofpaperand paper
board products. In particular, it is believed that Surprisingly
the shape factor ofthe kaolin, the coarseness ofthe calcium
carbonate,and/ortheamountofthickenerin thecoatingcom

US 2014/0370273 A1
position improve the modulus and stiffness of the coated
paper or paperboard product, and improve the flaking and
cracking at the fold of the coated product. For example, a
platy kaolinhavingashapefactoroflessthan70andaground
calcium carbonate (GCC) having a particle size distribution
in which less than about90% by weightofthe GCCparticles
and greater than about 60% by weight ofthe GCC particles
havean esd ofless than 2 micronsprovides improvements in
the modulusandstiffnessofthecoatedproductandimproved
flaking and/or cracking at the fold ofthe coated product. As
usedherein, "platy kaolin' meanskaolinhavingahigh shape
factor. In addition, a thickener present in an amount ranging
from about 0.1% to about 0.9% by active dry weight ofthe
coating composition provides improvements in the modulus
and stiffness of the coated product and improved flaking
and/or cracking at the fold ofthe coated product. The shape
factorofthekaolin, theparticlesizeofthecalcium carbonate,
and the amount of the thickener may each individually be
selected to improve the modulus and stiffness ofthe coated
product, and the flaking and/or cracking at the fold of the
coated product. Alternatively, the shape factorofthe kaolin,
the particle size ofthe calcium carbonate, and the amount of
the thickener may be collectively selected to improve the
modulus and stiffness ofthe coated product, and the flaking
and/or cracking at the fold ofthe coated product.
0044 Accordingto someembodiments, thekaolin maybe
producedby, forexample, treatinga raw particulate hydrous
kaolin mineral ofthe sedimentary type, forexample,araw or
partially processed kaolin clay of the type which occurs in
Georgia, USA.Theprocessedkaolin mayhaveapsdSuchthat
at least 80%, preferably at least 84%, by weight ofthe par
ticles have an esd Smaller than 2 micrometers (microns). In
certain embodiments,thekaolin mayhaveapsdSuch thatnot
lessthan 12%byweightoftheparticles,preferably from 15%
to 35%,especially 18% to26%,havean esd smallerthan 0.25
micron. Desirably, at least 60%, preferably at least 65% by
weighthaveanesd less than 1 micron. The meanparticleesd
may be from 0.3 micron to 0.8 micron, especially from 0.5
micron to 0.7 micron.
0045. Accordingto someembodiments, thepercentageby
weightofthekaolin particles havinganesdin therange from
0.75 micron to 0.25 micron ofthepigmentproductaccording
to the first aspect of the invention is 40% or greater, for
example, from40% to 50%.Theshapefactoroftheprocessed
kaolin may be at least 10, desirably at least 20, forexample,
from about 10 to about 70, orabout 20 to about 70, orabout
30 to about 70, orabout 40 to about 70, about 50to about70,
or about 60 to about 70.
0046 According to some embodiments, the raw particu
late hydrous kaolin may be processed to produce a kaolin
pigment according to an exemplary method comprising the
steps of: (a) mixing a raw or partially processed kaolin clay
with waterto forman aqueous Suspension; (b) Subjecting the
Suspension produced by step (a) to attrition grinding using a
particulate grinding medium by a process in which theaver
age shape factorofthe kaolin clay is increased by at least 10,
preferablyatleast 20, (c)separatingtheSuspension ofground
kaolin clay from theparticulategrinding medium; (d)obtain
ing a coarse component by classifying, forexample, using a
centrifuge, and (e) dewatering the Suspension of ground
coarse kaolin clay separated in step (c) to recover a kaolin
pigment therefrom.
0047 According to some embodiments, in step (a) the
kaolin clay may form from 20% to 70%, for example, from
Dec. 18, 2014
20% to 45%, ofthe treated suspension. The kaolin clay may
includeasedimentarykaolinclay,forexample,asedimentary
kaolin clay from Georgia, USA. The raw kaolin clay may
have a psd such that not more than about 40% by weight
consists ofparticles havingan esdlargerthan 10 microns and
not more than 50% by weight, forexample, from about 20%
to about 40% by weight, consists ofparticles having an esd
smaller than 2 microns. The shape factor ofthe kaolin clay
treated in step (a) may be less than 15, for example, in the
rangeoffrom about5 to about 10.Thus, theshape factormay
be increased by a differential ofat least 30, for example, at
least40,forexample, fromashapefactorvalueoflessthan 15
to a shape factor value greater than 55 (e.g., a shape factor
from about 60 or greater to less than about 70).
0048. When preparing an aqueous suspension of the
kaolin clay to be treated in step (a), according to some
embodiments, a dispersing agent for the kaolin clay may or
may not be added to the kaolin clay.
0049. The kaolin clay processed in step (a) ofthe method
accordingto Someembodiments, maybeacoarsecomponent
obtained from classifying, forexample, usinga centrifuge, a
standardblockysedimentarykaolin clay,forexample,having
a shape factor offrom about 5 to about 10. The coarse com
ponent may have not more than 50% by weight ofparticles
having an esd less than 2 microns and not morethan 10% by
weight having an esd less than 0.25 micron.
0050. According to some embodiments, the psd of the
kaolin clay may be adjusted by blending from about 99 to
about 50partsby weightofthekaolin clay with from about 1
to about 50parts by weight, forexample, from 10 to 30 parts
by weight, ofa fine platy kaolin component, in particular, a
fine platy component having a shape factor ofat least about
15, for example, from about 15 to about 40 and whose per
centages by weight ofparticles Smaller than 2 microns and
0.25 micronarerespectivelyatleastabout85% byweightand
at least about 20% by weight. The fine platy kaolin compo
nent may be a kaolin derived from either a primary or a
sedimentary deposit. According to Some embodiments, the
exemplary fine platy kaolin component may be added to the
kaolin ofor obtained from the coarse component prior to or
after the grinding step (b). The addition may be carried out
with the two kaolin components to beblended in eitherpow
dered, dry form, or in the form ofan aqueous Suspension.
0051. It has been determined that by producing a kaolin
product by blending in the manner described, the rheology
and dewatering characteristics ofan aqueous Suspension of
the kaolin processed in accordance with some exemplary
embodiments are improved, for example, providing
improved runnabilityandparticlealignmentwhen thekaolin
is used in a coating composition.
0.052 According to some embodiments, the kaolin clay
may be subjected to one or more well-known purification
stepstoremove undesirableimpurities,forexample,between
steps (a) and (b). For example, the aqueous Suspension of
kaolin clay may be subjected to a froth flotation treatment
operation to remove titanium containing impurities in the
froth. Alternatively, or in addition, the Suspension may be
passedthroughahigh intensity magnetic separatorto remove
iron containing impurities.
0053 According to some embodiments, step (b) may
include a process wherein the Suspension of kaolin clay is
treatedby mediumattritiongrinding,forexample,whereinan
energy offrom about 40 kWh to about 250 kWh per tonne of
clay (on a dry weight basis) is dissipated in the Suspension.

US 2014/0370273 A1
According to Some embodiments, step (b) may include a
processincludingatleasttwo stages, forexample,afirststage
(b1) wherein delamination ofthe kaolin clay occurs, and a
secondstage(b2)whereincomminution oftheplateletsofthe
kaolin clay occurs.
0054. Ithas been foundthat it may bebeneficial to subject
the Suspension ofthe kaolin clay to a relatively gentle com
minution step (b1), forexample, grinding usingaparticulate
grinding medium in orderto break down composite particles
that are present in the raw kaolin clay. Such composite par
ticles may generally include coherent stacks or blocks of
individual hexagonal plate-like particles, particularly where
the kaolin clay is from a sedimentary deposit. When the
kaolin clay is Subjected to relatively gentle comminution, for
example,bygrindingin Step (b1), the compositeparticles are
broken down to give the individual thin, substantially hex
agonal plates. Suchaprocess may generally be referred to as
'delamination, and has the result ofincreasing the average
shape factor ofthe kaolin clay. For example, this exemplary
process may increasetheshapefactorofthekaolin clay from
a starting shape factorofabout 5 to about 10to an increased
shape factor ofat leastabout 50 to 55 (e.g., from about 60to
less than about 70). As used herein, “relatively gentle grind
ing' means grinding in an attrition grinding mill with a par
ticulategrinding medium, the contents ofthe attrition grind
ing millbeingagitatedby meansofan impeller,which rotates
at a speed, which is insufficient to set up a Vortex in the
Suspension, inparticular,ataperipheral speedbelowabout 10
meters/second and in which theamount ofenergy dissipated
in the Suspension during grinding is less than about 75 kWh
per tonne, forexample, less than about 55 kWh per tonne, of
kaolin clay on a dry weight basis. The particulate grinding
medium may be of relatively high specific gravity, for
example,2 orgreater,and may, forexample, includegrains of
silica sand, where the grains generally have diameters not
larger than about 2 millimeters and not smaller than about
0.25 mm.
0055 According to some embodiments, stage (b2) ofthe
two stageform ofstep (b) in the method,thegrinding maybe
performed in an attrition grinding mill, which is equipped
with a stirrer capable ofbeing rotated at a speed such that a
VortexisformedintheSuspension in the millduringgrinding.
Theparticulate grinding medium may havea specificgravity
of2 or more, and may include grains ofsilica sand, wherein
the grains may generally having diameters not larger than
about2 mm andnot smallerthan about0.25 mm. Ifstage(b2)
is precededby a relatively gentle comminution in stage (b1),
the amount ofenergy dissipated in the Suspension ofkaolin
clay in stage (b2) may be in the rangeoffrom about 40 kWh.
to about 120kWhperdrytonneofkaolinclay. However, ifthe
relatively gentle comminution step (b1) is omitted, the
amount ofenergy dissipated in the Suspension ofkaolin clay
in step (b)ispreferably inthe rangeoffrom about 100kWhto
about 250 kWh per dry tonne ofkaolin clay.
0056. According to some embodiments of step (c), the
Suspension ofground kaolin clay may be separated from the
particulategrindingmediuminaknown manner,forexample,
by passing the Suspension through a sieve of appropriate
aperture size, for example, a sieve having nominal aperture
sizes in the range offrom about 0.1 mm to about 0.25 mm.
0057 According to some embodiments of step (d), the
Suspension ofground kaolin clay may be classified using a
centrifuge (e.g., Alfa Laval or Merco).
Dec. 18, 2014
0058. Following step (c), step (d)orstep (e), according to
some embodiments, the kaolin clay may be further treated to
improve one or more of its properties. For example high
energyliquidworking,forexample, usingahighspeedmixer,
may be applied to the product in slurry form, for example,
before step (e) orafter step (e) and Subsequent re-dispersion
in an aqueous medium, for example, during makedown ofa
coating composition.
0059. According to some embodiments, in step (e) the
Suspension ofground kaolin may be dewatered in one ofthe
ways well known in the art, for example, via filtration, cen
trifugation, evaporation, or the like. For example, use of a
filterpress maybemadeto formacakehavingawatercontent
in the rangeoffrom about 15% toabout35% by weight. This
cakemaybe mixed withadispersingagentforthekaolin clay
andthereby convertedintoa fluid slurry, which may betrans
ported and sold in this form. Alternatively, the kaolin clay
maybe thermally dried, forexample,by introducingthe fluid
slurry ofthe kaolin clay into a spray drierand thereby trans
ported in a substantially dry form.
0060 According to some embodiments, the kaolin prod
uct may haveaspecific Surfaceareaas measuredby the BET,
N, method ofat least 12 Square meters pergram (m/g), for
example, from 15 m/g to 20 m/g.
0061 According to certain embodiments, less than about
microns. For example, less than about 70% by weight and
greaterthanabout 60% by weight ofthe particles ofcalcium
carbonatehavean esdless than 2 microns.The mean particle
esd may be from 1 micron to 3 microns, especially from 1
micron to 1.35 microns.
0062. The particulate calcium carbonate used in certain
embodiments ofthe present invention may be obtained from
a naturalsourcebygrindingormaybeprepared synthetically
by precipitation, i.e., precipitated calcium carbonate (PCC),
or may be a combination ofthe two, i.e., a mixture ofthe
naturally derived ground material and the synthetic precipi
tated material. The PCC may also be ground.
0063 Ground calcium carbonate (GCC) is typically
obtained by grinding a mineral Source Such as chalk, marble
orlimestone, which may be followed by a particle size clas
sification step, in orderto obtaina producthavingthe desired
degree of fineness. The particulate solid material may be
ground autogenously, e.g., by attrition between the particles
ofthe solid material themselves, oralternatively, in the pres
enceofaparticulategrinding mediumcomprisingparticles of
a different material from thecalcium carbonate tobeground.
0064. Wetgrinding ofcalcium carbonate involvesthe for
mation ofan aqueous Suspension ofthe calcium carbonate
which may then be ground, optionally in the presence ofa
Suitable dispersing agent, for example sodium polyacrylate.
Reference may be made to, for example, EP-A-614948 for
more information regarding the wetgrinding ofcalcium car
bonate.Thedispersant usedforgrindingthe calcium carbon
ate may comprise, consist essentially of, or consist ofa non
ionic dispersant.
0065. After thegrinding has been carried out, the suspen
sion may be dewatered to a high Solids suspension, and any
grinding medium removed. Ahigh Solids suspension formed
by saiddewatering may suitably havea solids level ofat least
about 10wt % (forexample, at leastabout50wt %) to about
80 wt %, for example, up to about 78 wt %. The high solids
Suspension may be formed using a dispersing agent, for

US 2014/0370273 A1
example a non-ionic dispersant. The dispersing agent used
may or may not be the same as that optionally used in the
grindingstep. However,thedispersingagentusedatthepost
grinding stage may be added to restrict flocculation of the
particulate inorganic material in the high Solids Suspension,
andmaytypicallybepresentinadispersant-effectiveamount,
typically at least about 0.1% by weight ofthe dry inorganic
particulate material, or at least about 5% by weight. The
amount ofdispersing agent which may be present may be at
leastabout 0.3%toabout 1.5% byweightofthedry inorganic
particulate material. The amounts ofdispersing agent speci
fiedareparticularly suitable foruse in connection with GCC
and PCC.
0066. When the inorganic particulate material is obtained
from naturally occurringsources,itmaybethatSome mineral
impurities contaminate the ground material. For example,
naturally occurring calcium carbonate occurs in association
with other minerals. Also, in some circumstances, minor
additionsofotherminerals maybeincluded,forexample,one
ormore ofkaolin, calcined kaolin, wollastonite, bauxite, talc
or mica, could also bepresent. In general, however, the inor
ganic particulate material used in certainembodiments ofthe
invention maycontainlessthan 5%byweight,preferablyless
than 1% by weight ofother mineral impurities.
0067 PCC may be used as the source ofparticulate cal
cium carbonateinthepresentinvention,and maybeproduced
by any of the known methods available in the art. TAPPI
Monograph Series No 30, “PaperCoating Pigments, pages
34-35 describes the three main commercial processes for
preparing precipitated calcium carbonate which is Suitable
foruseinpreparingproductsforuseinthepaperindustry,but
mayalsobeusedinthepracticeofcertainembodimentsofthe
present invention. In all three processes, limestone is first
calcined to produce quicklime, and the quicklime is then
slakedin waterto yieldcalcium hydroxideor milkoflime. In
the first process, the milk oflime is directly carbonated with
carbon dioxide gas. This process has the advantage that no
by-product is formed, and it is relatively easy to control the
propertiesandpurity ofthecalcium carbonateproduct. In the
secondprocess,the milkoflimeiscontactedwith soda ash to
produce, by double decomposition, a precipitate ofcalcium
carbonate and a solution ofsodium hydroxide. The Sodium
hydroxideis substantially completely separated from thecal
cium carbonate ifthis process is to be commercially attrac
tive. Inthe third maincommercialprocess,themilkoflime is
first contacted with ammonium chloride to give a calcium
chloride Solution and ammonia gas. The calcium chloride
solution is thencontacted with sodaashtoproduce, bydouble
decomposition,precipitatedcalcium carbonateandasolution
ofsodium chloride.
0068. The PCC may be formed into a cake (e.g., a filter
cake), which comprises atleast about 70 wt% solid content,
the remainderbeing water. A dispersant (forexample, a non
ionic dispersant or an anionic dispersant) may be combined
directly with thecake and,optionally, water may beadded to
the cake before the dispersant is added.
0069. The process for making PCC results in very pure
calcium carbonate crystals and water. The crystals can be
producedina variety ofdifferentshapesandsizes, depending
on the specific reaction process that is used. The three main
forms of PCC crystals are aragonite, rhombohedral, and
scalenohedral, all of which are suitable for use in certain
embodiments of the present invention, including mixtures
thereof.
Dec. 18, 2014
0070 According some embodiments, the kaolin and cal
cium carbonates described herein may be used as a pigment
productinapaperorpaperboardproductcoatingas described
herein.
0071. According to certain embodiments, the ratio of
kaolin to calcium carbonate may range from about 20:80 to
about 80:20, or from about 30:70 to about 70:30, or from
about 40:60 to about 60:40.
0072 Accordingtosomeembodiments, acoatingcompo
sition for use in producing coatings on paper or paperboard
products and other Substrates may include an aqueous Sus
pension ofa particulate pigment together with a hydrophilic
adhesive or binder, wherein the particulate pigment may
include a combination ofkaolin and calcium carbonate, for
example, precipitated and/or ground calcium carbonate
(GCC). For example, the solids content ofthe paper coating
composition may be greater than about 60% by weight, for
example, at least about 70%, or as high as possible, but still
providing a suitably fluid composition that may be used in
coating. According to Some embodiments, the coating com
position may include a dispersing agent, for example, up to
about 2% by weight of a polyelectrolyte based on the dry
weight ofpigment present. For example, polyacrylates and
copolymers containing polyacrylate units may be used as
suitable polyelectrolytes. The kaolin and calcium carbonate
accordingto someembodiments may beused on theirown in
the coating composition, orthey may be used in conjunction
withoneormoreotherknownpigments, suchas,forexample,
calcined kaolin, titanium dioxide, calcium sulphate, satin
white, talc, and so called “plastic pigment.” When a mixture
ofpigments is used, the kaolin and calcium carbonate pig
ment product according some embodiments may be present
in the mixtureofpigmentsinan amountofatleastabout80%
ofthe total dry weight ofthe mixed pigments.
0073. According to some embodiments, the binder ofthe
coating composition may include an adhesive derived from
natural starch obtained from a known plant source, for
example, wheat, maize, potato, or tapioca, although it is not
essential to use starch as a binder ingredient. Other binders,
which may be used with or without starch, are mentioned
later.
0074 According to some embodiments, the starch
employed as abinderingredient may beeitherunmodified or
raw starch, or it may be modified by one or more chemical
treatments. For example, the starch may be oxidized to con
vert some of its —CH-OH groups to —COOH groups. In
Some cases the starch may have a small proportion ofacetyl,
—COCH groups. Alternatively, the starch may be chemi
cally treated to renderitcationic oramphoteric, in particular,
with both cationic and anionic charges. The starch may also
be converted to a starch ether or hydroxyalkylated starch by
replacing some —OH groups with, for example,
—O—CH2—CH-OH groups, —O—CH2—CH groups or
—O—CH2—CH2—CH2—OH groups. A further class of
chemically treated starches that may be used is the starch
phosphates. Alternatively, the raw starch may be hydrolyzed
by means ofa dilute acid oran enzyme to produce a gum of
the dextrin type.
0075 Accordingto someembodiments, theamountofthe
starch binder used in the coating composition may be from
about4% to about25%by weight,basedonthedry weightof
pigment. The starch binder may be used in conjunction with
one or more otherbinders, for example, synthetic binders of
thelatexorpolyvinylacetateorpolyvinylalcoholtype. When

US 2014/0370273 A1
the starch binder is used in conjunction with anotherbinder,
for example, a synthetic binder, the amount of the starch
bindermaybefromabout2%toabout20%byweight,andthe
amount ofthe synthetic binder from about 2% to about 12%
by weight, both based on the weight of dry pigment. For
example, at least about 50% by weight ofthe binder mixture
includes modified or unmodified starch.
0076 According to some embodiments, a method ofuse
ofthe coatingcomposition may include applyingthe coating
composition to a sheet ofpaper or paperboard and calender
ing the paper or paperboard to form a gloss coating thereon.
Accordingto someembodiments,theglosscoatingisformed
on oneorboth sides ofthepaperorpaperboard. Accordingto
Some embodiments, calendering may include passing a
coated paper sheet or paperboard between calender nips or
rollers one or moretimes to improvethepaperorpaperboard
Smoothnessandglossandreducethebulk.Accordingtosome
embodiments, elastomer coated rollers may be employed to
give pressing ofhigh solids compositions, and elevated tem
perature may be applied, and/or five or more passes through
the nips may be performed.
0077 According to some embodiments, paper or paper
board after coating and calendering may have a total weight
perunitareain therange30g/m to 70g/m,forexample,49
g/m to 65g/m or35g/m to 48g/m.Thefinal coatingmay
haveaweightperunitareapreferablyfrom3g/m to20g/m.
forexample,from 5 g/m to 13 g/m. Such acoating maybe
appliedtobothsidesofthepaper.Accordingtosomeembodi
ments, the paper gloss may be greater than 45 TAPPI units,
and the Parker PrintSurfvalueatapressureof1 MPa ofeach
paper coating may be less than 1 micron.
0078. The gloss ofa coated paper or paperboard surface
may be measured by means of a test laid down in TAPPI
Standard No 480 ts-65. The intensity oflight reflected at an
anglefrom theSurfaceofthepaperorpaperboardis measured
and compared with a standard of known gloss value. The
beamsofincidentand reflectedlightarebothatanangleof75
degreestothenormaltotheSurface.Theresultsareexpressed
in TAPPI gloss units. According to some embodiments, the
gloss ofthepigmentproduct maybegreaterthanabout50, for
example, greater than 55, TAPPI units.
0079. TheParkerPrintSurftest provides a measure ofthe
Smoothness ofa paper Surface, and includes measuring the
rate at which air under pressure leaks from a sample ofthe
coatedpaperorpaperboardwhich is clamped, underaknown
standardforce,betweenanupperplate,whichincorporatesan
outlet for the compressed air, and a lower plate, the upper
surface ofwhich is covered with a sheet ofeither a soft or a
hardreference Supporting materialaccording tothe nature of
thepaperorpaperboardbeing tested. From therate ofescape
oftheair,aroot mean cubegap in micronsbetween thepaper
Surface and the reference material is calculated. A smaller
valueofthis gap represents a higher degree ofSmoothness of
the Surface ofthe paperbeing tested.
0080 According to some embodiments, the adhesive or
binderofthecoatingcompositionmay form from 4%to30%,
for example, from 8% to 20% (e.g., from 8% to 15%) by
weight ofthe Solids content ofthe coating composition. The
amount employed may depend on the coating composition
andthetype ofadhesive, which may itselfincorporateone or
more ingredients. Forexample, hydrophilic adhesives incor
porating one or more of the following adhesive or binder
ingredients may be used in the following Stated amounts: (a)
latex: levels ranging from 4% by weight to 20% by weight
Dec. 18, 2014
(the latex may include, for example, a styrene butadiene,
acrylic latex, vinyl acetate latex, or styrene acrylic copoly
mers); and (b) other binders: levels ranging from 4% by
weight to 20% by weight. Examples ofotherbinders include
casein, polyvinyl alcohol, and polyvinyl acetate.
I0081. Additives in various classes may, depending on the
type ofcoating composition and/or material to be coated, be
included in the coating composition. Examples of Such
classes ofoptional additives are as follows:
0082 (a)cross linkers, for example, in levels up to 5%
by weight (e.g., glyoxals, melamine formaldehyde res
ins, ammonium Zirconium carbonates);
0.083 (b)water retention aids, forexample, in levels up
to 2% by weight (e.g., sodium carboxymethyl cellulose,
hydroxyethyl cellulose, PVA (polyvinyl acetate),
starches, proteins, polyacrylates, gums, alginates, poly
acrylamidebentonite, and othercommercially available
products sold for Such applications);
0084 (c) viscosity modifiers or other thickeners, for
example, in levels up to 2% by weight (e.g., polyacry
lates, emulsion copolymers, dicyanamide, triols, poly
oxyethylene ether, urea, Sulphated castor oil, polyvinyl
pyrrolidone, montmorillonite, sodium alginate, Xanthan
gum, Sodium silicate, acrylic acid copolymers, HMC
(hydroxymethyl celluloses), HEC (hydroxyethyl cellu
loses));
0085 (d) lubricity?calendering aids, for example, in
levelsup to2%by weight(e.g., calciumStearate,ammo
nium Stearate, zinc stearate, wax emulsions, waxes,
alkylketene dimer, glycols);
I0086 (e)dispersants,forexample, inlevels upto2%by
weight (e.g., polyelectrolytes, suchaspolyacrylatesand
copolymers containing polyacrylate species, for
example,polyacrylatesalts (e.g., sodium andaluminum
optionally with a Group II metal salt), sodium hexam
etaphosphates, non-ionic polyol, polyphosphoric acid,
condensed sodium phosphate, non-ionic Surfactants,
alkanolamine, and other reagents commonly used for
this function);
0.087 (f) antifoamers/defoamers, forexample, in levels
up to 1% by weight (e.g., blends ofsurfactants, tributyl
phosphate, fatty polyoxyethylene esters plus fatty alco
hols, fatty acid soaps, siliconeemulsions and othersili
conecontainingcompositions,waxesandinorganicpar
ticulates in mineral oil, blends of emulsified
hydrocarbons, andothercompounds soldcommercially
to carry out this function);
0088 (g) dry or wet pick improvement additives, for
example, in levels up to 2% by weight (e.g., melamine
resin, polyethylene emulsions, urea formaldehyde,
melamine formaldehyde, polyamide, calcium Stearate,
styrene maleic anhydride, and others);
0089 (h) dry or wet rub improvement and abrasion
resistance additives, for example, in levels up to 2% by
weight (e.g., glyoxal based resins, oxidized polyethyl
enes, melamine resins, urea formaldehyde, melamine
formaldehyde, polyethylene wax calcium Stearate, and
others);
0090 (i) gloss-ink hold-out additives, for example, in
levels up to 2% by weight(e.g., oxidizedpolyethylenes,
polyethylene emulsions, waxes, casein, guar gum,
CMC, HMC, calcium stearate, ammonium stearate,
Sodium alginate, and others;

US 2014/0370273 A1
0091 ()optical brightening agents (OBA)and fluores
cent whitening agents (FWA), forexample, in levels up
to 1% by weight (e.g., stilbene derivatives));
0092 (k) dyes, for example, in levels up to 0.5% by
weight;
0093 (1)biocides/spoilagecontrol agents, forexample,
in levels up to 1% by weight (e.g., metaborate, sodium
dodecylbenene Sulphonate, thiocyanate, organosulphur,
Sodium benzonate, and other compounds sold commer
cially forthisfunction,forexample,the rangeofbiocide
polymers sold by Calgon Corporation);
0094 (m) levelling and evening aids, for example, in
levels up to 2% by weight (e.g., non-ionic polyol, poly
ethylene emulsions, fatty acid, esters, and alcohol
derivatives, alcohol/ethylene oxide, sodium CMC,
HEC, alginates, calcium Stearate, and other compounds
sold commercially for this function);
0.095 (n) grease- and oil-resistance additives, for
example, in levels up to 2% by weight (e.g., oxidized
polyethylenes, latex, SMA (styrene maleic anhydride),
polyamide, waxes, alginate, protein, CMC, and HMC);
0096 (o) water-resistance additives, for example, in
levels up to 2% by weight(e.g., oxidizedpolyethylenes,
ketone resin, anionic latex, polyurethane, SMA, gly
oxal, melamine resin, urea formaldehyde, melamine
formaldehyde,polyamide,glyoxals, Stearates,andother
materialscommercially availableforthis function); and
0097 (p) insolubilizer, forexample, in levels up to 2%
by weight.
0098. Foralloftheabove-listedadditives,thepercentages
by weight provided are based on the dry weight ofpigment
presentin the composition. Wheretheadditive ispresent in a
minimum amount, the minimum amount may be 0.01% by
weight based on the dry weight ofpigment.
0099. According to some embodiments, the substrates
may be coated either on a sheet forming machine (i.e., "on
machine’) or “off-machine' on a coater or coating machine.
Use of high solids coating compositions may be desirable
because Such compositions tendto leaveless waterto evapo
rate following the coating process. However, Solids levels
should not be high enough to createhigh viscosity and level
ling problems.
0100. According to some embodiments, the coating
method may include (i) a means of applying the coating
composition to the Substrate being coated, for example, an
applicator, and(ii)a meansforensuringthata desiredlevel of
coating composition is applied, for example, a metering
device. When an excess ofthe coatingcomposition is applied
totheapplicator,themeteringdevicemay beprovideddown
stream oftheapplicator. Alternatively, the correct amount of
coating composition may be applied to the applicatorby the
metering device, forexample, as afilm press.Atthepoints of
coatingapplication and metering, a backing roll (e.g., one or
twoapplicators) ornothing (i.e., webtension) maybeusedto
Supportthe Substrate being coated. Thetimethecoating is in
contact with the substratebefore theexcess coating is finally
removed (i.e., thedwell time) may beshort, long,orvariable.
0101 According to some embodiments,the coating com
position may be added by a coating head ata coating station.
Accordingtothequalityofcoatingdesired,theSubstratemay
be single coated, double coated, and triple coated. When
providing morethan one coat, the initial coat (i.e.,apre-coat)
may have a cheaper formulation and optionally less pigment
inthecoating composition.Acoaterthatisapplyingadouble
Dec. 18, 2014
coating(i.e.,acoatingoneachsideoftheSubstrate), mayhave
two orfourcoatingheads, depending on the number ofsides
coated by each head. Some coating heads coat only one side
atatime, butsomeroll coaters (e.g., film press,gate roll, size
press) may coat both sides ofthe Substrate in a single pass.
0102) Examples ofcoaters that may be employed in step
(b) include air knife coaters, blade coaters, rod coaters, bar
coaters, multi-head coaters, roll coaters, roll/blade coaters,
castcoaters, laboratory coaters,gravure coaters, kiss coaters,
liquidapplication systems, reverse roll coaters,andextrusion
COaterS.
0103) According to some embodiments of the coating
compositions described herein, water may be added to the
solids to provide a concentration of solids, which when
coated onto a sheetto a desiredtarget coat weight, thathas a
rheology suitable for the composition to be coated with a
pressure(e.g.,abladepressure)ofbetween about 1 andabout
1.5 bar. For example, the solids content may be from about
60% to about 70% by weight.
EXAMPLES
0104. In order to evaluate coating compositions, typical
paperboard used in the packaging industry was used as a
Substrate or base stock. Sample coating compositions con
taining selected platy clay and carbonate pigments were
applied to the paperboards using a CLC (Cylindrical Lab
Coater) machine. The sample coating compositions were
applied on one side ofthe paperboard, and the samples were
double-coated (i.e., a base coat and a top coat). The coated
sample paperboards were then calendered, and bending
modulus and stiffness tests wereconducted on thecoatedand
calendered paperboard samples. The samples were creased
along machine and cross direction using a CreaseStream.
Thereafter, the creased samples were folded using a rubber
roller to mimic the creasing and folding in an industrial or
manufacturing environment.
0105. The failure occurring at the creased or folded path
was observed undera microscope, and images weretaken So
that visual ratings oftheflaked andcrackedareas at the folds
couldbe made. Thecorrelationbetween the visual ratings for
flaking and cracking tendency and the bending modulus and
stiffness was evaluated.
0106 Sample hydrous kaolin pigments having different
shape factor, steepness, and particle size distribution were
evaluated. Table 1 below shows the physicalpropertiesofthe
sample kaolin pigments used in different tests described
herein. The shape factors provided for the kaolin pigment
samples were determined using the technique describedpre
viously herein. The particle size distributions for the kaolin
pigment samples were measured using Sedigraph technique
described previously herein.
TABLE 1
Sedigraph Shape
Pigments PSD 9% <0.25 m Steepness Factor
Kaolin Sample 1 (KS1) 21 33 62
Comparative Kaolin 21 19 75
Sample 1 (CKS1)
Sample 2 (CKS2)
Sample 3 (CKS3)

US 2014/0370273 A1
0107 The kaolin pigment samples were combined with
calcium carbonate pigment samples (i.e., ground calcium
carbonate (GCC)), and the combined pigment samples were
slurried at desired solids levels as mentioned in the tables
hereinassociatedwiththerespectivetests. Forthepurposesof
thetesting,thebasecoatweightwaskeptat 13g/m,andthe
top coat weight waskept at 10g/m. The following compo
nents werealso included in the sample coating compositions
tested: polyvinyl acetate-based binder (i.e., Resyn 1103
obtained from Celanese Emulsions); acrylic binder (i.e.,
Rhoplex P-308 obtained from Rohm and Haas); carboxym
ethyl cellulose (CMC) thickener(i.e., FINNFIX 30 obtained
from METSA Specialty Chemicals); carboxymethyl cellu
lose (CMC) thickener (i.e., FINNFIX 10 obtained from
Noviant); hydrophobically-modified alkali swellable emul
sion (HASE) thickener (i.e., Rhoplex RM232D obtained
from Rohm and Haas); acrylic-based emulsion copolymer
thickener (i.e.,Alcogum L29 obtainedfrom Alco Chemical):
andcoatinglubricant(i.e., Berchem 4095obtained from Ber
cen, Inc.).
Experimental Methods
0108. In order to assess the flaking and cracking charac
teristics ofthe samples, paperboard samples werecoatedand
tested. The coated paperboards were calendered at 175
poundspersquare inch (psi) pressure, 150 degrees F. using a
BeloitModel750Calender.Thecoatingsamples werekeptin
aTAPPI conditioned room forat leasttwenty-four hoursand
thereafter creased using a CreaseStream machine. The
samples werecreasedalongthe machineandcrossdirections,
and were thereafter folded in the direction away from coated
side first and then towards coated side to obtain visually
notable difference in the fractures occurring at the folded
area. Thefoldswere madeusinga 500gram rubberroller.The
samples were thereafter flattened out, and images of the
cracking-flaking tendency were taken using a microscope.
0109. A team ofeightto ten people were trained to assess
the cracking and flaking results using a visual ranking
method, with a rating of 1 being the best, a rating of5 being
average, and a rating of 10 being the worst. The team was
provided with reference images associated with each ofthe
rating values to comparethe tested samples with these refer
ence images to obtain more accurate results through the
visual ranking method. The average cracking and flaking
ratings were reported foreach sample tested.
0110. The following factors were considered for visual
assessmentofcrackingandflakingtendency,forcracking: (1)
Pigments
Dec. 18, 2014
theoverall sizeofthecracks; (2)the length ofcracks; and (3)
the number of cracks; and for flaking: (1) the chunks of
coating layers missing; (2) the coating particles loosely held
at the folded area; and (3) the coating layer about to flake
across the folded region.
0111. In order to assess the strength ofthe sample paper
boards coated with the tested coating samples, the samples
were tested according to a simply supported beam theory,
with each sample Supported at opposite ends with a concen
trated loadappliedat the midpointbetween the supports. See
FIG. 1, which shows a schematic ofthetestingarrangement,
where Pistheloadappliedatthecenterofthesample, Listhe
length ofthesample, E istheelastic modulus, I isthe moment
ofinertia, and 6 is the amount ofdeflection.
0112 Thebending resistance measurements were carried
outon coated paperboards pertheASTM D790-B method. A
ThwingAlbertEJAseriesinstrument witha 10Nloadcelland
MAP-Motion Analysis Presentation software was used to
collect the raw data. The strengthofthe tested material could
beunderstoodwith thehelp ofbendingtest results. Raw data
ofamount ofload applied to the sample and the associated
deflection was recorded using theThwingAlbertinstrument.
Loadanddisplacementreadings within theinitial segment of
theload-displacementgraph wereconsideredforthestiffness
calculations to betterdifferentiatethesamples.The forcewas
applied to each sample in the x-y plane. Within the elastic
range it can be observed that the loadand displacement rela
tionship is linear. This initial region is may be instructive as
the crack initiation may begin in this region.
0113. During testing, each sample was placed spanning
two Supporting aluminum anvils. It is noted that sample
paperboards were coated on the CLC, calendered, and con
ditioned before conducting the bending tests. The force is
appliedatthe centerofeachtest sample,andtheresistance of
each sample totheappliedbending force was recorded. Each
ofthe samples was kept in a TAPPI conditioned room forat
least twenty-four hours before conducting bending tests.
Each sample had the dimensions of 1 inchx3 inches.
0114) Effort was made to investigate whether better dis
ruption of the pigment packing structure may reduce the
modulus or stiffness of the samples. The effect of varying
GCC coarseness in the coating layer on mechanical proper
ties and its impact on flaking and cracking tendency was
studied. Table 2 below shows the coating formulations
included in this test. The coating drawdowns were taken on
Mylar film using a Precision coater. RL003 Polish MT/DF
Mylar drafting film manufactured by Grafix was used as a
base Substrate in this experiment.
TABLE 2
Components
Comparative
Ground Calcium
Carbonate 1
(CGCC1)
CKS2
CKS1
Comparative
Ground Calcium
Carbonate 2
(CGCC2)
Comparative
Ground Calcium
Carbonate 1
(GCC1)
50
50
50
50 50
50
50
50
50

US 2014/0370273 A1
TABLE 2-continued
Components i1A #2A #1 #2
Comparative
Ground Calcium
Carbonate 3
(CGCC3)
Binder PWAc1103 2O 2O 2O 2O
Thickener RM 232 O45 O.45 O45 O45
Ec 2.0 1.8 1.9 1.3
CGCC1, CGCC1, CGCC2, GCC1,
CKS1 CKS2 CKS2 CKS2
0115 FIG. 2 shows that exemplary embodiments ofhigh
shapefactorplatyclays likeCKS2andCKS1 showedalower
modulus withGCC1 compared toCGCC1 when blendedin a
50:50, clay:carbonate ratio. These results were based on the
lab scale drawdown study, but the overall graph shows a
significant difference in the modulus results between
samples. Based on these results, further testing was con
ducted using the CLC machine to mimic the commercial
coating application process and validate the effects ofGCC
coarseness on bending resistance and folding ability of the
paperboards.
0116. Theeffectofincreasing the level ofthickenerin the
coating compositions on flaking and cracking tendency was
tested to determine whether the hold out oftop coat can be
Components
CGCC4
GCC1
CGCC1
CKS3
CKS1
CKS2
KS1
PVAC 1103
Pigments
Binder
Lubricant
Thickener RM-232
improved so thatthe moreopenbasecoat is notreinforcedby
the top coatpenetration. Details ofthetested coating compo
sitions are provided in Table 3 below.
TABLE 3
Components BC1 TC1 TC2 TC3 TC4
Pigments Comparative 30 30 30 30
Ground
Calcium
Carbonate 4
(CGCC4)
CKS3 70 70 70 70
CGCC1 50
CKS2 50
Binder PVAC 1103 15 2O 2O 2O 2O
Lubricant Berchem 4095 0.7 0.7 0.7 0.7
Thickeners RM-232 O.367 O O.O7 O.15 O.25
Finnfix 10
Finnfix 30
0117 Comparing the results, it was observed that flaking
and crackingtendency inthecross direction was moresevere
than in the machine direction. It was also found that increas
ing the RM232 thickenerlevel reduces the severity ofcrack
Berchem 4095
Dec. 18, 2014
#3
50
2O
O.45
2.4
CGCC3,
CKS2
ing and flaking in the machine direction. Comparing the two
CMC types, theone with the higher molecular weight (Finn
fix 30) provided slightly improved flaking and cracking
results.
0118. Theeffects ofcoating compositions were tested for
a number of samples to determine the factors affecting the
modulus and stiffness of the coating compositions. The
mechanical strength properties of the paperboards coated
with a base coat only and paperboards coated with atop coat
and a basecoat were studied to determine the responseofthe
single and double coating layers on the flaking and cracking
tendency. Table 4 below shows the different pigment blends
used in this testing and other composition details.
TABLE 4
BC1 BC2 BC3 BC4 BCS BC6 TC1 TC2 TC3 TC4
30 1OO 100 8O
50 50 50 50
50 50
70 2O
50 50
50 50
50 50
15 15 15 15 15 12 2O 2O 15 15
0.7 0.7 0.7 0.7
O45 0.45 0.45 0.45 0.45 0.45 0.1 O.1 O.25 0.25
0119. As shown in FIG. 3, there is slight reduction in the
modulus in case ofbase coat compositions including GCC1
relative to base coat compositions including Carbital 60. As
shown in FIG. 4, the bending stiffness (IE) ofthe coatings
containingGCC1 areslightlylowerthanthebendingstiffness
of coatings containing CGCC1. Base coat compositions
including GCC1 and KS1 at a lower latex level provided
lower stiffness results. FIG. 5 shows that the paperboards
coated with the coating composition including Carbital
70:CKS1 as a base coat provided slightly lower bending
modulus values than the coating composition base coats
includingCarbital60:CKS1.AsshowninFIG. 6,thestiffness
ofpaperboardscoatedwiththecoatingcompositionbasecoat
including GCC1:CKS1 provided slightly lower values com
pared to the coating composition base coat including
CGCC1:CKS1.
0.120. Thecoating compositions identified in the horizon
tal legends of FIGS. 7 and 8 are listed in order of lowest
bending modulus on the left-hand top corner (CGCC4 top
coat/GCC1/CKS2 base coat) to the highest modulus on the
right-hand bottom corner (CGCC4:Kao91 30:70 top coat
High Latex/CGCC1:CKS1 basecoat).Theflakingandcrack
ing tendency ofthe coatedpaperboards is shown with respect

US 2014/0370273 A1
to the bending modulus results. Although the data points in
FIGS. 7 and 8 are scattered, there is a clear distinction
between base coat compositions containing GCC1 and
CGCC1. Overall, the base coat compositions containing
GCC1 tend to reduce the severity offlaking and cracking. A
higher latex content in the top coat compositions appears to
improvetheflakingand crackingperformance. However, the
base coat compositions have a stronger influence on flaking
and cracking compared to the top coat compositions.
0121. In addition, different base coat compositions were
tested to evaluate whether the bindercould be reduced while
stillreducingflaking.Theselectionofbasecoatpigments was
based on the testing results mentioned previously herein.
Paperboards were coated on the CLC, standard paper tests
were conducted, and flaking and cracking tendency ratings
were made.
0122) The following pigment samples were tested with
respect to the folding ability ofthe coated paperboards: (1)
KS1; (2) CKS2; (3) CKS1; (4) CGCC1; and (5) GCC1. The
following variables were tested with respect to the folding
ability ofthe coated paperboards: thickener variation, KOH
dispersion, coat weight variation, binder level (PVAc at 22,
19, and 16 parts). PVAc-Acrylic (at 11 and 11 parts), and
bindertype (PVAc and PVAc-Acrylic). The results shown in
Table5below werenormalizedwithconstantcoatweightand
actual thickener levels using general regression.
TABLE 5
Components BC1 BC2 BC3 BC4 BC5 BC7 BC9
Pig- CKS2 50 50 50
ments CKS1 50 50
KS1 50 50
CGCC1 50 50 50 50 50
GCC1 50 50
Binders PVAc 1103 11 11 22 22 11 11 11
BASF P3O8 11 11 11 11 11
Thick- Alcogum O45 0.53 0.4O O.452 O.49 0.58 0.64
ele L29
Components BC17 TC
Pigments CKS2 50
GCC1 50
CGCC4 70
CKS3 30
Binder System
PVAC 1103 - P3O8
Binder (11 + 11 parts)
PVAC 1103
Binder (22 parts)
PVAC 1103
Binder (16 parts)
Dec. 18, 2014
TABLE 5-continued
Binders PVAC 1103 16 11
BASF P3O8 11
Lubricant Berchem 4095 0.7
Thickener Alcogum L29 O.34 O.12
I0123 FIG. 9 shows that lower flaking and cracking ten
dency could be achieved at increased thickener levels in the
basecoatcompositions. Similarresults wereobservedforthe
experiment carried out earlier, where thickener levels were
increased in the top coat compositions. Asshown in FIG. 10,
a slight reduction in the bending stiffness values with an
increase in the thickener level explains the reduced flaking
and cracking tendency observed at higherthickener levels.
0.124 Referring to FIGS. 11 and 12, although a few data
points are scattered, the trend lines indicate that flaking and
crackingratingsincreasewithanincreaseinbasecoatweight.
Thus, levels ofbase coat weight may be adjusted to achieve
desirable impact on the flaking and cracking tendency.
(0.125. As shown in FIG. 13, pigment blends GCC1/KS1
and CGCC1/KS1 with PVAc1 103:Acrylic P308bindershow
lowerbending modulus and flaking tendencyas compared to
the control CGCC1/CKS1 composition with PVAc1 103:
Acrylic P308binder.Also, flakingresultsoftheGCC1/CKS2
compositions are superior to the control CGCC1/CKS2.
0.126. As shown in FIG. 14, formulations GCC1/KS1 and
CGCC1/KS1 with PVAc1103:Acrylic P308 11+11 parts of
binder showed lower bending modulus values and improved
crackingtendencyas comparedtothecontrolCGCC1/CKS1.
It can be observed from FIG. 14 that the correlation between
bending modulus and cracking performance is weak.
I0127. As shown in FIG. 15, the bending stiffness results
for GCC1/KS1 and CGCC1/KS1 with PVAc1103:Acrylic
P308 11+11 parts ofbinder are lower than the control and
have better flaking tendency than the control composition
CGCC1f(CKS1.
I0128 FIG.16 shows thatthecorrelationbetweencracking
tendency and bending stiffness is weak. However, coating
compositions GCC1/KS1 andCGCC1/KS1 with PVAc1 103:
Acrylic P308 11+11 parts of binder showed consistent
improvements in the cracking tendency at lower stiffness.
I0129. Table 6 below shows average flaking and cracking
results, bending modulus, and stiffness measurements ofthe
sample coating compositions.
TABLE 6
Bending
Bending Stiffness
Modulus (GPa) (Ibf in. sq)
Avg. Avg. Normalized Normalized
Pigment Flaking Cracking with Coat with Coat
Blends MD MD Weight Weight
CGCC1,4350 4 6 2.4 O.O29
GCC1 KS1 4 5 2.9 O.O29
CGCC1 KS1 4 5 2.6 O.O29
GCC1, CKS2 5 5 2.4 O.O29
CGCC1, CKS2 6 8 2.1 O.O29
CGCC1, CKS1 5 6 3.4 O.O3O
CGCC1, CKS2 7 8 2.4 O.O29
CGCC1, CKS1 5 6 3.6 O.O3O
GCC1, CKS2 6 8 3.1 O.O31

US 2014/0370273 A1
0130 Table 7 below shows the sample coating composi
tions that improved flaking and cracking performance ofthe
paperboards compared to the respective control composi
tions.
TABLE 7
Flaking Cracking
Control Forms Possible Solutions Tendency Tendency
Compare with Control CGCC1,CKS1 5 6
Control CGCC1,CKS1 GCC1 KS1 4 5
CGCC1 KS1 4 5
Compare with Control CGCC1,CKS2 6 8
Control CGCC1,CKS2 GCC1,CKS2 5 5
0131 Based on the testing, the sample coating composi
tions includingCGCC1/KS1 andGCC1/KS1 provided lower
flaking and cracking tendency than the control composition
includingCGCC1/CKS1.Thebending modulusandstiffness
results ofthese samples were significantly lower than ones
coated with the control composition CGCC1/CKS1. Flaking
and cracking tendency results of the sample compositions
including GCC1/CKS2 were better than the control compo
sition CGCC1/CKS2. Changing only the carbonates in the
control coating composition CGCC1/CKS2 showed signifi
cant improvements in the flaking and cracking tendency.
0.132. As shown bythetest results,GCCcoarsenessseems
tohaveaneffect onthe modulusand stiffness ofthecoatings.
Thepacking structure within the coating layerand alignment
ofhigh shape factorplaty clays may havea strong influence
onthein-planestrength propertiesofthecoatinglayer. GCC1
in combination with clays in thebase coats improved flaking
and cracking results compared to thebase coat compositions
containing CGCC1. The composition containing KS1 in the
base coats at a lowerlatex level provided improved results at
Some instances compared to the base coats including CKS1.
Aslightlyhigheramountoflatexcouldbeusedtoimprovethe
cracking and flaking tendency. The composition including
KS1 pigment inthebase coatcompositions may improve the
foldingabilityatnormalorslightly reducedbinderlevels.The
testing also shows that coating compositions having slightly
higherthan normal thickener levelsprovideimprovedoverall
folding ability ofthe paper grades.
0133. Accordingto Someembodiments, a coatingcompo
sition may include kaolin having a shape factor ofless than
about 70, and calcium carbonate having a mean particle size
(ds)ofatleastabout 2.4 micronsanda steepnessfactorofat
leastabout30. Forexample,thedo maybegreaterthanabout
2.6 microns, greater than about 2.8 microns, or greater than
about 3.0 microns. According to some embodiments, the
steepnessfactor(e.g.,do/dox100)maybegreaterthanabout
32, greaterthan about34, greaterthan about 36, greaterthan
about 40,orgreaterthan about 43. Someembodimentsofthe
coating may contain ground calcium carbonate having the
Pigments
Dec. 18, 2014
11
exemplary particle size distribution shown below in Table 8.
The composition in Table 8 will be referred to as “GCC2.”
TABLE 8
Sedigraph 5100 GCC2 Composition
<10 m (%) 98 wt.%
<5 m (%) 81 wt.%
<2 m (%) 40 wt.%
<1 m (%) 13 wt.%
<0.5 m (%) 2 wt.%
<0.25 m (%) 1 wt.%
d30 1.7 m
dso 2.6 m
d70 4.0 m
Steepness Factor 43
BET Surface Area
I0134. It can be seen from Table8 that the median particle
size (ds)ofGCC2 is relatively large,about2.6 microns.The
overall particlesizedistributionofGCC2 also hasa relatively
high steepness factor ofat least about 30, specifically about
43. GCC2 was classified to remove the coarsest particles,
resulting in a greater percentage ofparticles having an esd
lessthanabout 10microns,whilestill maintainingagenerally
coarse particle size distribution. The overall coarse particle
size distribution is also indicated by the relatively low per
centageoffineparticles (e.g.,particles withanesd lessthan 1
micron).
0.135 The coarser, narrow GCC particle size distribution
in GCC2 may have a significant effect on the bending stiff
ness and folding ability of double coated paper and paper
boards when used ina coating, Suchasabase coat.As shown
in Tables 9 and 10, several coating formulations were pre
pared by blending different platy clays with GCC2 at 50:50
(Table 9) and 25:75 (Table 10) clay-to-carbonate ratios. The
blendedclay-carbonatebasecoatswereevaluatedonSmooth
ness and folding performance when placed on a Substrate.
Purecoatings with 100percentofCGCC1, GCC2,andCKS2
werealsoevaluatedto understandthecoatingstructure,bend
ing stiffness, and its effects on the folding ability.
0.136. As describedabove, thebinderand thickenerlevels
may impact thefoldingabilityofthecoated substrates. Thus,
whenevaluatingtheclay-GCC2compositions, thebinderand
thickener levels ofthebase coats were keptconstant. Thetop
coatformulation wasalso keptconstant. Toevaluatetheclay
GCC2 compositions, SBS base boards were double-coated
on a CLC machine. All coatings were prepared at optimum
solids and at about 8.5 pH. For the purposes oftesting, the
basecoatweightwaskeptconstantat 13g/m andthetopcoat
waskeptconstantat10g/m.Allthesampleswerecalendered
before testing.
TABLE 9
Pigments Base Coat Formulations
KS1 50 25
CKS1 50 25
KS3 50
KS2 50
CKS2 50

US 2014/0370273 A1
TABLE 9-continued
GCC2 50 50 50 50 50 50 75
CGCC4
CKS3
KS4 50
Binders
Lubricant Berchem 4095
Thickener L29 O.45 0.45 0.45 0.45 0.45 0.45 0.45
TABLE 10
Pigments KS1
CKS1
KS3 25
KS2 25
CKS2 25 1OO
CGCC1 100
GCC2 75 75 75 75 100
CGCC4
CKS3
KS4 25
Binders PVAC 1103 11 11 11 11
BASF P3O8 11 11 11 11
Lubricant Berchem 4095
Thickener L29 O.45 0.45 0.45 0.45
0.137 FIG. 17 shows the folding performance ratings for
each of the clay-GCC2 compositions, as compared with
CGCC1, CKS2, and two control compositions. As shown in
FIG. 17,compositionscontainingGCC2pigmentsinthebase
coats showed improved folding performance ofthe samples
compared to the other blends tested in the series ofexperi
ments without GCC2, described above. Except for the KS4/
GCC2 and KS3/GCC2 compositions at 50:50 ratio, all other
blendsshowedimprovedfoldingabilityoverthecontrol coat
ings (e.g., Cntrl. CKS2/CGCC1 and Cntrl. CKS1/CGCC1).
Theimprovedfoldingratings obtainedforthecoatingformu
lations were within the range of 1 to 5, and generally within
the range of 1 to 4.
0.138. As shown in FIG. 17, the base coat blends with
KS1/GCC2 at 50:50 and 25:75 ratios and CKS1/GCC2 at
25:75 ratio showed improved folding performance and
smoothness compared to 100% GCC2 and control formula
tions.Also, someblends, suchasCKS1/GCC2at 50:50 ratio,
showed a Substantial improvement in Smoothness, while
other blends, such as CKS2/GCC2 at 50:50 ratio, showed a
slight improvement in Smoothness while maintaining com
parable folding performance when compared to the 100%
GCC2 blend. Although CKS2/GCC2 at 25:75 ratio blend
does not appear to show any significant improvement in the
smoothnessascomparedto the 100%GCC2 blend,thisblend
showedthe best foldingperformance results compared to the
rest ofthe group.
0139 FIG. 18 shows the bending stiffness results for the
coatings described inTables 9 and 10, where 100% CGCC1
was used in the base coat formulation. The bending stiffness
results in FIG. 18 suggest that samples coated with KS1/
GCC2 blends (e.g., 50:50 and 25:75 ratios) have a higher
bending stiffness when compared to other clay-carbonate
blends included in the experiment. Without being limited by
theory, it ispossible thatthebulky structureofcoatingblends
PVAC 1103 11 11 11 11 11 11 11
BASF P3O8 11 11 11 11 11 11 11
Dec. 18, 2014
75
11
11
O45
Top Coat
70
30
11
11
0.7
O.12
containing KS1 pigments may contribute to the slightly
higherbending stiffness oftheseblends. Comparing stiffness
results ofFIG. 18 and results described above (e.g., FIGS. 4
and 6), the overall range ofstiffness values oftheplaty clay
GCC2 forms appear to be slightly lower than the platy clay
CGCC1 blends.
0140 FIG. 19 shows a comparison of the bulk for platy
clay-carbonate blends described above for both CGCC1 and
GCC2. FIG. 19 shows that KS1/Carbonate blends tend to
impartabulkierstructureat50:50& 75:25 ratioscomparedto
other clay-carbonate blends. From FIG. 19, it also appears
that 100% GCC2, having coarser carbonate pigments,
imparts a bulkier structure than 100% CGCC1. Standard
GCC, such as CGCC1 containing higher percentage of fine
particles, for example, less than 2 microns, may provide
denserpackingthan a narrowerparticlesize distribution with
coarserpigments, such as GCC2. Similarly, thebulky nature
ofblends containing KS1 maybe useful in hidingbase paper
irregularities and achieving improved Smoothness and light
Scatter.
0141 FIGS. 17-19 suggest that the KS1/GCC2 blend
combination may providean optimum packing structure that
is required for improved folding ability and mechanical
strength properties. Forexample, the formulations with KS1
in the base coats showed improved folding performance
results consistently in each ofthe experimental results dis
closed herein. From the results described in FIGS. 17-19, it
appears that KS1 in combination with GCC2 provides
improved Smoothness and folding performance without
affecting the bending stiffness ofthe coated samples.
0.142 Generally, it appears that the KS2, CKS2, CKS1,
and KS1 platy clay pigments blended with GCC2 showed
improvedSmoothnessandfoldingperformancerelativetothe
same platy clay pigments blended with CGCC1. Changing
the base coat formulations from 100% CGCC1 to 100%

US 2014/0370273 A1
GCC2alsoappearsto improvetheSmoothnessofthecoating,
but the folding performance may be compromised to some
extent. Itisalso importantto notethatcomparedtothecontrol
formulations, the 100% GCC2 coating showed enhanced
folding performance and comparable Smoothness.
0143. The sample coated papersubstrates were tested for
mercury porosity. FIG.20shows mercuryporosity results for
the coatedpaperSubstrates. Mercury porosimetry is a widely
used technique for characterizing pore size distributions and
pore Volume measurements. Mercury does not wet the paper
surface. In this test method, mercury is intruded into the
sample by increasing pressure in discrete steps. The Volume
ofmercuryintrudedintheporestructurecorrelatestothepore
volume and pore size distribution.
0144. As shown in FIG. 20, different clay-carbonate pig
ments selectedaccording to theirdistinctphysical properties
gave significantly different coating structures. The total
intruded pore Volume results are dependent (sometimes sig
nificantly) on the base coat pigment blends. Some embodi
ments result in a pore Volume ranging from 0.4 to 0.6 cubic
centimeterspergram (cm/g),forexample,ranging from 0.4
to 0.41 cm/g, 0.41 to 0.42cm/g, 0.42to 0.43 cm/g, 0.43 to
0.44 cm/g, 0.44 to 0.45 cm/g, 0.45 to 0.46 cm/g, 0.46 to
0.59 cm/g, or 0.59 to 0.60 cm/g.
0145 Thecoating porestructure is mainly determined by
the base coat formulations. Total intruded volume results
showed coating structure differences caused due to basecoat
blends. FIG. 20 shows that the narrow particle size distribu
tion coarsercarbonatepigments likeGCC2 in the base coats
bring greater structuring capabilities. By replacing CGCC1
with GCC2 in the base coats, higher pore volume was
obtained. The overall increase in pore volume may be ben
eficial for reducing flaking and cracking tendency of the
coatings. Mercury porosimetry results also correlate to the
bulk results reported in FIG. 19. While not wishing to be
bound by theory, it appears that bulkier coating structures
having higher pore Volume may tend to reduce the stress
exertedbythecoatinglayersduringbendingorfoldingopera
tions.Thus, the results show that it may bepossible to modu
late the base coat formulations to achieve desired coating
structure and folding ability.
0146. Otherembodiments willbeapparentto thoseskilled
in theart from consideration ofthe specification andpractice
ofthe embodiments disclosed herein. It is intended that the
specification andexamples be consideredasexemplary only.
1. A coating composition comprising:
kaolin having a shape factor less than about 70; and
calcium carbonate, whereinlessthan about 90%by weight
andgreaterthan about 60% by weightofparticlesofthe
calcium carbonate have an esd less than 2 microns.
2. Thecomposition ofclaim 2, further comprising a thick
C.
Dec. 18, 2014
3. The composition of claim 2, wherein the thickener is
by active dry weight ofthe composition.
4-5. (canceled)
6. The composition of claim 2, wherein the thickener is
selectedfrom thegroup consistingofalkali-solubleemulsion
polyacrylate thickeners, hydrophobically-modified alkali
soluble emulsion polyacrylate thickeners, and CMC (car
boxymethyl celluloses) thickeners.
7. The composition ofclaim 1, wherein less than about
micron.
8-10. (canceled)
80% by weight of the kaolin has an esd less than about 1
micron.
12. (canceled)
microns.
14-17. (canceled)
18. A paperboard product comprising the coating compo
sition of claim 1 on at least one Surface ofthe paperboard
product.
19. A coating composition comprising:
kaolin having a shape factorless than about 70; and
calcium carbonate having a ds of at least about 2.4
microns and a steepness factor ofat least about30.
20. The composition of claim 19, further comprising a
thickener.
21. The composition ofclaim 20, wherein thethickeneris
by active dry weight ofthe composition.
22-23. (canceled)
24. The composition ofclaim 20, wherein thethickeneris
selectedfrom thegroup consistingofalkali-solubleemulsion
polyacrylate thickeners, hydrophobically-modified alkali
soluble emulsion polyacrylate thickeners, and CMC (car
boxymethyl celluloses) thickeners.
micron.
26-28. (canceled)
80% by weight of the kaolin has an esd less than about 1
micron.
30. (canceled)
31. The composition of claim 19, wherein the calcium
carbonate has a do ofat least about 2.6 microns.
32-33. (canceled)
34. The composition of claim 19, wherein the calcium
carbonate has a steepness factor ofat least about 32.
35-41. (canceled)
42. A paperboard product comprising the coating compo
sition ofclaim 19 on at least one surface ofthe paperboard
product.

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