Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

Effects of water-soluble cellulosic polymers on coating development and quality
Hitomi HAMADA, Toshiharu ENOMAE, Izumi SHIBATA, Akira ISOGAI and Fumihiko ONABE
Paper Science Laboratory
Graduate School of Agricultural and Life Sciences
The University of To kyo
JAPAN

ABSTRACT

Recently, ‘environmentally friendly’ has gained more importance for paper industry than before. In this study,
a water-soluble biodegradable polymer produced from cellulose was applied as a coating constituent. The
polymer applied was cellouronic acid with almost all primary alcohol groups at C-6 oxidized selectively tocarboxyl groups. The influences of several water-soluble polymers, i.e., cellulosic polymers including
cellouronic acid, starch and polyvinyl alcohol, upon binder migration and coating characteristics werestudied. Infrared spectra and energy dispersive X-ray analysis of scanning electron microscopy exhibited thatthe binder latex was distributed uniformly across the coating containing cellulosic polymers in the thickness
direction. These effects were not observed with starch or polyvinyl alcohol. Coatings containing cellulosic
polymers provided good coating surface properties, that is, high porosity and high light scattering efficiency,
which can lead to good printability. Biodegradable cellulosic polymers are capable to give both good
recyclability and good printability to coated paper.

Keywords: Binder migration, Cellouronic acid, CMC, Coating, Starch, Water-soluble polymer

INTRODUCTION

Binder migration meaning that binder latex concentrate near the top surface of coating layer occurs
occasionally in a drying process for coated paper. Binder migration may harm significantly coating surface
properties such as porosity and optical properties, and printability. Binder migration is affected by manyfactors; base paper properties, coating color compositions, wet coating structure, coating application method,1

Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

etc. It was reported1,2) that starch formulated in coating colors induced binder latex migration. In this study,
the effect of water-soluble cellulosic polymers formulated as a coating additive on binder migration wasstudied and compared with the effect of other water-soluble polymers, i.e., starch and polyvinyl alcohol. A
water-soluble biodegradable cellulosic polymer, polyglucuronic acid (cellouronic acid) sodium salts, wasalso applied as a coating additive.

EXPERIMENTAL

Water-soluble polymer samples
Cellulosic polymers used were anionic polymers with carboxyl groups, i.e. cellouronic acid andcarboxymethyl cellulose (CMC), and nonionic polymers, i.e., hydroxyethyl cellulose (HEC) andhydroxypropyl cellulose (HPC). Cellouronic acid with almost all primary alcohol groups at C-6 oxidized
selectively to carboxyl groups (Fig. 1) was prepared from regenerated cellulose with 2,2,6,6,-tetramethylpipelidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems 3). Its degrees of substitution andpolymerization were about 1.0 and 55, respectively. Six grades of sodium salt types of CMC (Finnfix 5, 30,
300, Noviant, Finland and Cellogen PL15, WS-A, F-SB, Dai-ichi kogyo seiyaku, Japan) with different
degrees of substitution or polymerization were used as shown in Table 1.

Three kinds of starch, i.e., starch phosphate (P -140, Oji Cornstarch, Japan), oxidized starch (Ace C, Oji
Cornstarch, Japan) and TEMPO-oxidized starch prepared from commercial oxidized starch (Ace C) with
TEMPO-NaBr-NaClO systems, and amylopectin were compared. These were compared also to polyvinyl
alcohol (PVA110, Kurare, Japan) as a synthetic water-soluble polymer.

Coating
The coating colors at 50 wt% solids containing the water-soluble polymers were prepared. One pph of eachwater-soluble polymer were added separately to 100 pph of precipitated calcium carbonate (Brilliant-15,
Shiraishi kogyo, Japan) in slurry with 10 pph of carboxylated SB-latex (LX407G, Nippon Zeon, Japan) as abinder. Viscosity of the coating colors diluted to 25 wt% solids was measured using a Brookfield viscometer.
All measurements were performed at a fixed shear rate of 132 s-1 at 23 °C for 5 minutes. The coating colors
at 50 wt% solids were drawn down on a PET film (140 g/m2 ) with a wire bar (No. 14). The coat weight
ranged around 18 g/m2 . The coatings on a film were dried immediately for one minute using a hot-air dryer.
2Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

Binder migration
Attenuated Total Reflection (ATR) measurements using an infrared absorption spectrometer (MAGNA-IR
860, Nicolet) were performed to determine the binder latex content near the coating surface. Figure 2 is an
example of IR spectrum of coating surface measured by ATR method using a ZnSe crystal with 45° incident
angle. The binder latex content near the coating surface was evaluated as a ratio of absorbance of SB-latex at
700 cm-1 to that of calcium carbonate at 874 cm-1 . These wave numbers come from conjugated double bondsof the benzene ring in SB-latex and molecular vibration of calcium carbonate, respectively 4).

The distribution of binder latex in coating cross-sections was examined with scanning electron microscope(SEM). The binder latex of coatings was tagged with osmium by exposing the samples to osmium tetraoxide(Wako Chemicals, Japan) vaper for 12 hours. Cross sections of the coatings were set on SEM mounts andcoated with platinum. Osmium mapping images over cross sections of coatings were obtained using an
FE-SEM (S-4000, Hitachi, Japan) with energy dispersive X-ray (EDX) analyzer (EMAX-5770, Horiba,
Japan). The conditions for this mapping method were 20 kV accelerating voltage, 30 s scanning time for ascan, 40 accumulation scans, 256×256 pixels image size for SEM with 40×256 pixels in the center scannedarea for osmium mapping.

Porosity and light scattering coefficient
Porosity and light scattering coefficient of the coatings were measured. Porosity was determined by amercury buoyancy method. This method is to determine the pore volume from coating solid volume andapparent coating bulk obtained by measuring buoyancy of the sample immersed in mercury. The coating
samples on film were prepared by drying at 50 °C in advance. Here, the coating solid volume was calculated
as a sum of the masses each constituent formulated in the coating colors divided by true density. The lightscattering coefficient of the coatings was calculated with the Kubelka-Munk equation from the two kinds ofreflectance of the coating over two substrates with different reflectances5).

RESULTS AND DISCUSSION

Viscosity
Table 2 shows viscosities of the coating colors containing several water-soluble polymers. When starch3

Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

phosphate, oxidized starch or PVA were included in the coating colors, their viscosities showed much lower
values than that of no water-soluble polymer. The viscosity of coating colors containing cellulosic polymers
showed relatively high values and increased with increasing the degrees of polymerization or substitution at
CMC. These cellulosic polymers may interact with pigment or binder latex and form a network structure. In
the case of clay-based coating6), the wet coating structure was expressed with a figurative illustration as a
network formed by the shear thinning bridging of adsorbed CMC with solution CMC.

Binder migration
Figure 3 shows the binder latex content near the coating surface obtained by ATR measurements for several
kinds of coatings with water-soluble polymers. The surface binder latex contents of the coatings with CMC
and cellouronic acid showed low values. SEM photographs with osmium, namely, binder latex distributionof a cross-section of coatings without water-soluble polymer (A) and with CMC (B) were shown in Fig.4.
The binder latex in the coating without water-soluble polymer was higher at the coating surface than inside
the coating, whereas the binder latex was distributed uniformly across the coating with CMC in the
thickness direction. When the values of absorbance ratio obtained by ATR measurement is higher than thevalue of coating with CMC shown in Fig. 3, the binder latex is rich at the parts close to the coating surface.
From these results, it is suggested that CMC or cellouronic acid can prevent binder migration to the coating
surface.

Figure 5 shows the surface binder latex content of the coatings with some kinds of CMC. Because theabsorbance ratio of SB-latex to calcium carbonate showed almost the same values irrespective of the degrees
of polymerization or substitution, the difference of these parameters of CMC commonly used in paper
coating did not affect the binder migration. The viscosity of coating color also did not affect bindermigration because the viscosity was dependent on the degrees of polymerization or substitution, cf. Table 2.
According to general considerations7) , greater binder migration is expected with more stably dispersed
colors with low viscosities than less stably dispersed colors with high viscosities because more stable colors
tend to have more free liquid than less stable systems until they become immobilized. However, bindermigration was induced by amylopectin formulated to the coating color with high viscosity as shown in Fig. 3
and Table 2, this contradicts the above theory.

With the view of investigating the influence of electric charge of water-soluble polymers upon bindermigration, anionic cellulosic polymers with carboxyl groups, i.e., CMC and cellouronic acid, and nonionic4Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

cellulosic polymers, i.e., HEC and HPC, were compared. When cellulosic polymer, irrespective of presenceof carboxyl groups with it, was included in the coating color, the binder latex did not migrate to the coating
surface as shown in Fig. 6. This finding means that electronic charge of cellulosic polymers did not affectbinder migration. Ikeda et al 2) investigated about the effect of starch on binder migration and reported that
there was no difference in binder migration between anionic starch phosphate and nonionic hydroxyl ethyl
starch. Furthermore, TEMPO-oxidized starch with almost all primary alcohol groups at C-6 oxidized
selectively to carboxyl groups prepared by TEMPO-NaBr-NaClO systems was compared with commercial
oxidized starch and starch phosphate. None of those kinds of starch prevented the binder migration to thecoating surface. (Fig. 7) These results suggest that the chemical interactions between carboxyl groups ofwater-soluble polymers and anionic site of binder latex or pigment were not a main factor to affect thebinder migration.

From these results, it became evident that the viscosity of coating colors and the electronic charge ofwater-soluble polymers formulated in coatings do not effect the binder migration, and linear polysaccharides
as cellulosic polymers, irrespective of presence of carboxyl groups with it, have effect in preventing bindermigration. This agree with the result obtained by other authors8) that addition of polymer, sodium alginate,
CMC or PVA, to the paper coatings inhibited binder latex migration, the order of effectiveness in reducing
surface latex concentration was alginate > CMC > PVA. Alginate is a linear polysaccharide formed by the
ß-1,4 linkage which is similar in structure to cellulose. The structural properties of linear polysaccharides
were predicted to somehow exert influences on the binder migration mechanisms.

Porosity and light scattering coefficient
Table 3 shows the porosity and light scattering coefficient of coatings. The two parameters of the coatings
with CMC or cellouronic acid showed higher values than that of any of the coatings without water-soluble
polymers, or with starch or PVA. It is suggested that flocculated structure coming from the interaction
between these cellulosic polymers, pigment and/or binder latex contributed to the high porosity of thecoatings. A large solid/air interface areas coming from high porosity provides more light scattering. In
practice, coatings formulated with CMC or cellouronic acid showed higher light scattering efficiency. Rennel
et al9) reported that a small amount of CMC led to a minor increase in the porosity of coating based on theplastic pigments. For the clay-based coating10), CMC-addition caused a significantly larger increase in theporosity. In that case, it was suggested that pigment flocculation contributed to the higher porosity inaddition to a retarded particle reorientation during the consolidation.
5

Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

Coatings containing CMC or cellouronic acid showed high porosity and high light scattering efficiency. As
these cellulosic polymers also have effect in preventing binder migration, water-soluble cellulosic polymers
can be expected to work as a coating agent to control the coating properties.

CONCLUSIONSIn this study, the influence of several water-soluble polymers upon binder migration that occurs duringdrying and characteristics of the coating were studied. A water-soluble biodegradable polymer from cellulose,i.e., cellouronic acid, was applied as a coating constituent.

High viscosities of coating colors containing cellulosic polymers suggested that the cellulosic polymers
might interact with pigments or binder latex and form a network structure. The binder latex content near thecoating surface and its distribution over a coating cross-section were examined by ATR measurements andline analysis using FE-SEM/EDX. When anionic cellulosic polymers were included in the coating colors,
the binder latex did not migrate to the coating surface and was distributed uniformly across the coating in the
thickness direction. These effects were not observed with starch, irrespective of presence of carboxyl groups
with it, or polyvinyl alcohol, but observed with nonionic cellulosic polymers. From these results, it became
evident that the viscosity of coating colors and the electronic charge of water-soluble polymers formulated incoatings do not effect the binder migration. Linear polysaccharides as cellulosic polymers, irrespective ofpresence of carboxyl groups with it, have effect in preventing binder migration resulting in binder latex
distribution uniformly across the coating in the thickness direction.

Coatings containing CMC or cellouronic acid showed high levels of porosity and light scattering coefficient.
The interaction between these cellulosic polymers and pigment and/or binder latex might contribute to thehigh porosity of the coatings, and large solid/air interface areas coming from high porosity provided more
light scattering, which leads to good printability. Therefore, cellulosic polymers are capable of becoming aprintability enhancer. Furthermore, development of recyclable -coated paper with good printability can be
expected using biodegradable cellulosic polymers.

6

Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

ACKNOWLEDGMENT

The authors wish to thank Dr. Masato Kato, Ryukoku University, for his contribution in the line analysis
using FE-SEM/EDX. We are also grateful to Dr. Akio Okagawa, IMERYS Minerals Japan, and Dr. Hiroshi
Sata, Oji Cornstarch, for offering CMC and starch samples, respectively.

REFERENCES

1

Kline, J. E., 1993 Advanced Coating Fundamentals Symposium proc., Tappi Press, Atlanta, USA, 93(1993)

2

Ikeda, A., Enomae, T. and Onabe, F., Japan Tappi, 55 (2) 82 (2001)3

Isogai, A. and Kato, Y., Cellulose 5 (3) 153 (1998)

4

Tachibana, T., Fujihira, S., Shigetomi, K. and Nagai, K., Japan Tappi, 46 (11) 96 (1992)

5

Hamada, H., Enomae, T., Onabe, F. and Saito, Y., Japan Tappi, 55 (11) 79 (2001)

6

Whalen-Shaw, M., Gautan, N., 1990 Coating Conference proc., Tappi Press, Boston, USA, 371 (1990)

7

Whalen-Shaw, M. et al, Binder Migration in Paper and Paperboard Coatings, Tappi Press, chapter 2(1993)

8

Steven, G., 1991 Coating Conference proc., Tappi Press, Atlanta, USA, 221 (1991)

9

Rennel, C., Eriksson, U. and Rigdahl, M., Nordic Pulp and Paper Research J., no. 4, 254 (1994)

10 Eriksson, U. and Rigdehl, M., 1993 TAPPI Advanced Coating Fundamentals Symposium proc., 19(1993)

7

Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

Table 1 CMC samples used in this study
Degree ofDegree of
Brookfield viscosityNO.
substitution
polymerization(mPa·s), 25 °C
1
0.8
110
10 (2%)2
0.8
360
30 (2%)
30.8
480
300 (2%)4
0.45~0.55
460~500
15 (1%)
5
0.7~0.8
460~500
750 (2%)
6
0.85~0.95
460~500
200 (2%)
Manufactures: 1~3; Noviant, 4~6; Dai-ichi kogyo seiyaku

Table 2 Viscosity of coating colors
Water-soluble
Brookfield viscosity
polymer(mPa·s), 25 wt% solids
None
17
CMC 1
22
CMC 2
25
CMC 3
28
CMC 4
30
CMC 5
38
CMC 6
32
HEC
24
HPC
24
Cellouronic acid15
Starch phosphate
3
Oxidized starch4
Amylopectin
36
PVA
4

Table 3 Properties of coatings
Water-soluble
Specific scattering
Porosity (%)
polymercoefficient (m2/kg)
None
46
173
CMC 2
50
182
Cellouronic acid49
202
Starch phosphate
47
141
PVA
46
173

8

Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

Fig. 1 Cellouronic acid

Absorbance

874

700

950

850

750

650

Wave number (cm-1)
Fig. 2 IR spectrum of coating surface measured by ATR method

SB-latex/CaCO3, absorbance ratio

0.1
0.08
0.06
0.04
0.02
0
Non

CMC 2

Cellouronicacid

Starch Amylopectine
phosphate

PVA

Water-soluble polymer
Fig. 3 Surface binder latex content of the coatings with several kinds of water-soluble polymers

9Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

A

B

2 µm

Fig. 4 SEM photographs with latex distribution of a cross-section of
coatings. A: no water-soluble polymer, B: CMC formulated

SB-latex/CaCO3, absorbance ratio

0.1
0.08

0.06
0.04

0.02
0
Non

CMC 1

CMC 2

CMC 3

CMC 4

CMC 5

CMC 6

Water-soluble polymer
Fig. 5 Surface binder latex content of the coatings with some kinds of CMC

10

Hamada, H., Enomae, T., Shibata I., Isogai, A. and Onabe, F. , “Effects of water soluble cellulosic polymers on coating development and quality”,
Proceedings of PITA Coating Conference, Edinburgh, Great Britain (March 4-5, 2003) 91-95

SB-latex/CaCO3, absorbance ratio

0.1
0.08
0.06
0.04
0.02
0
Non

CMC 2

Cellouronic
acid

HEC

HPC

Water-soluble polymer
Fig. 6 Surface binder latex content of the coatings with cellulosic
polymers

SB-latex/CaCO3, absorbance ratio

0.1
0.08
0.06
0.04
0.02
0
Non

Starch phosphate

Commercial
oxidized starch

TEMPOoxidized starch

Water-soluble polymer
Fig. 7 Surface binder latex content of the coatings with some kindsof starch11