A NOVEL METHOD FOR DETERMINING AMOUNT OF INK PRINTED ON PAPER
USING X-RAY FLUORESCENCE SPECTROSCOPY
Hitomi Hamada, Toshiharu Enomae, Masato Kato* and Fumihiko Onabe
Paper Science Laboratory, Graduate school of Agricultural and Life Sciences,
The University of Tokyo, Tokyo, JAPAN, e-mail: hitomi@psl.fp.a.u-tokyo.ac.jp*

Digital Archives Research Center, Ryukoku University, Shiga, JAPANABSTRACTINTRODUCTION

With the view of quantifying amounts of ink

There are two major known methods toprinted on paper for offset printing, a newly

quantify amounts of ink on nip-printed paper, one isdeveloped technique using an X-ray fluorescence

to measure the amount of ink transferred bymethod was applied. In this technique, the content

weighing the ink roll before and after printing; theof copper included in a cyan-ink printed on paper

other is to measure the print density using a

was evaluated from an intensity of its peak in the

spectrophotometer. However, the graph in the

X-ray fluorescence spectrum. A cyan-ink, one of thearticle 1) on ink receptivity of coated paper permits

four colors of process inks (C, M, Y and Bk ), is

to interpret that the print density was notoften used in printability tests. By the X-ray

proportional to the amount of ink transferred over 1

fluorescence method, mass of ink, preferably at

g/m2 ink amount. Lepoutre2) reported that there

large amounts, on paper can be measured precisely

were the exceptions of the supercalendered coating

for a short period of time, though they are notand the latex-covered coating though the optical

proportional to the print density. As an application

density of the prints was only a function of theof this technique, the X-ray intensities of thequantity of ink deposited for a variety of coatingselements contained in printed samples with andother than that at low inking levels.

without print mottles were measured and mapped

In this study, a novel technique to quantify

using an X-ray fluorescence microanalyzer. Fromamounts of ink on nip-printed paper using an X-ray

the results of this measurement, it was suggested

fluorescence method was developed. For thisthat the distribution of coating components near thetechnique, a particular attention was focused on asurfaces is one of the important factors affecting ink

cyan-ink, one of process inks, often used inmottling. The amount of ink transferred was foundprintability tests. The novel technique by an X-ray

to decrease with increasing the smoothness of paper

fluorescence method was found to measurein the case of offset printing. As the amount of ink

precisely amounts of cyan-ink transferred on papertransferred reflects the properties of paper, it isfor a short period of time.

expected that the X-ray fluorescence based
quantifying method of ink on paper assists inestimating the printability of a variety of printing
papers.

8.04 keV is proportional to the content of copper

EXPERIMENTAL

included in a cyan-ink. A process cyan-ink usedconventional is composed of Cu-phthalocyanin (Fig.

Samples
Woodfree paper (65 g/m2 , Mitsubishi Paper3) 3). The calibration line for converting the X-ray

Limited,paper

intensity of copper to the amount of ink transferred(uncalendered, about 10 g/m2 coat weight, 65 g/m2

was derived. The X-ray intensity of copper wasbasis weight) both commercially available were

evaluated as a value of a difference between counts

supercalendered at 50 ℃, for 2 nips under linear

per time and per current at 8.04 keV for printed andpressures of 19.6, 49, 98, 147 and 196 kN/m.

unprinted surfaces.

Mills

Japan)

andcoatedTwelve kinds of paper samples with several levelsof smoothness were prepared. Bekk smoothnessCa

Cu(Oken, Modified Bekk method, Digital EY type,Cl

KRK, Japan) and 75 °sheet gloss (Glossmeter
GM-26D, Murakami Color Research Laboratory,
Japan) of the papers were measured. Printing on
the papers with several levels of smoothness wereconducted on a universal printability tester (MPT
8000, KRK, Japan) with a conventional process
cyan-ink (TK high echo, Tack 9.5, Toyo Ink, Japan)
for offset. Printing on groundwood paper (53 g/m2 ,

Al

Fe

Si

Cu

Fig. 1 X-ray fluorescence spectrum of printed surfaceCa

Dai-ni paper, Japan) and recycled paper (60 g/m2 ,Cl

Oji Paper, Japan) were also conducted under thesame conditions. The amount of ink transferred
was measured by weighing the ink roll before andafter printing and was found to range from 1.0 to
10 g/m2 .

Si
AlQuantifying

methodofamount

of

ink

Fe

Fig. 2 X-ray fluorescence spectrum of unprinted surface

transferred by X-ray fluorescence analysis
The X-ray fluorescence spectrum of eachsample having several different amounts of ink
transferred, which are known by weighing the ink
roll, was measured using an X-ray fluorescenceanalyzer(MESA-500,

Horiba,Japan)

under

conditions of 50 kV tube voltage, 74~240 µA tube
currents, 5 mm diameter for scanning area and 250
s for scanning time. Figures 1 and 2 are examples of
the X-ray fluorescence spectrum of printed andunprinted surfaces. The X-ray intensity of Cu-Kα at

Fig. 3 Pigment Blue (Cu-phthalocyanine)Comparison between X-ray fluorescence method,where L* g is lightness of unprinted surface and L* isand optical density measurement
The

X-ray

fluorescence∆D = log L* g − log L*

methodwaslightness of printed surface

compared with the optical density measurement.
Seven kinds of coated papers with several different

Application for ink mottling analysis

levels of lightness were prepared. Coating colors

Two kinds of cyan prints with coated papers

were preliminaly formulated with 70 pph of kaolin(about 10 g/m2 coat weight, 105 g/m2 basis weight)

clay (UW-90, Engelhard, USA), 30 pph of calcium

prepared under different drying conditions, i.e. acarbonate (Brilliant-15, Shiraishi kogyo, Japan) andpoor print with print mottle (Fig. 4 A) and a good

10 pph of binder latex (LX407G, Nippon Zeon,

print (Fig. 4 B), were compared. Surface roughness

Japan). Two types of pigment latex, anionic hollow

of unprinted parts of the prints was measured using

sphere pigment (HP-1055, Rohm and Haas, Japan)

a stylus profilometer (SE-3, Kosaka laboratory,

and anionic filled one (V1004, Nippon Zeon, Japan)

Japan). The X-ray intensities of copper andwere added separately to this color. The amounts ofelements (Ca, Al and Si) contained in the prints

pigment latex were 5, 10 and 20 pph. The coatings

were measured and mapped using an X-ray

were drawn down on one side of a base sheet

fluorescence microanalyzer (EAGLEⅡ, EDAX,

2

Japan). The measuring conditions of mapping were

(Woodfree paper, 65 g/m , Nippon Paper Industries,
Japan) with a wire bar using a sheet-fed coater
equipped

withasynchro-starting

dryer

A

(PM9040MC, SMT, Japan). The coat weight was
targeted at 9 g/m2 . The coated papers were dried at
120 ℃ for 10 s, and supercalendered at 50 ℃
under a linear pressure of 49.1 kN/m. Printing on
coated papers was conducted on a RI printing tester(Ishikawajima Sangyo Kikai, Japan) with a

1 mm

conventional process cyan-ink for offset. RI
printing tester permits comparison of every sample
within the same run under the same conditions ofB

nip pressure, speed and ink volume on a plate.
The amounts of cyan-ink printed on thecoated papers prepared were determined by thefluorescencemethod.

The

spectral

distribution of printed and unprinted surfaces were
measured using a spectrophotometer under the

460 µmX-ray

600 µmconditions of D 65 diffuse illuminant / 2 °normal
observer. Lightness (L* ) was derived from the4)

Fig. 4 Poor (A) and good (B) printed surfaces

spectral distribution by basic equations . The

observed by stereo microscope with 9

following equation gave the differences of optical

rectangular parts showing measured

density between printed and unprinted surfaces.

area using FE-SEM/EDX

40 kV tube voltage, 900 µA tube current, 512×400

that the sheet gloss of the coated paper increased

pixels and 400 ms scanning time for one pixel. With

with increasing the smoothness and then leveled off.

the view of analyzing an area closer to the printedThis is probably due to a decrease in refractive

surfaces, the X-ray intensities of elements contained

index caused by the collapse of coating at highin the prints which were platinum-coated inpressures. The refractive index of the substance isadvance for providing electric conductivity were

one of the factors affecting gloss. The amount of

measured with nine areas of 600×460 µm of each

ink transferred decreased with increasing theprint (Fig. 4) using an FE-SEM (S-4000, Hitachi,smoothness of papers as shown in Fig. 7. This result

Japan) with EDX (EMAX-5770X, Horiba, Japan) at

is consistent with those obtained by other

20 kV accelerating voltage, 0.20 nA probe current

authors5,6).

2

and 500 s scanning time.
Bekk smoothness (s) ［Coated］
0

RESULTS AND DISCUSSION

500

1000

1500

2000

2500

90
80

Relationship between smoothness of paper and70

Figure

5

shows

that

the

75°glossamount of ink transferredsmoothness

increased by supercalendering for both coated anduncoated papers. The smoothness of coated paper

60

Uncoated

50

Coated4030

was higher than that of uncoated paper at the same

20

linear pressure. The smoothness of coated paper

10increased as linear pressure increased up to 15000kN/m and above this value it decreased. This factindicates that flocs in the paper became protruded

50
100
150
Bekk smoothness (s) ［Uncoated ］
Fig. 6 Gloss measured in MD vs Bekk
smoothness

on the paper surface. Therefore, the smoothness of
paper decreased at high pressures. Figure 6 shows
0
140
120

2000

100
1500

80

1000

60
CoatedUncoated

500

40
20

0
0

50

100
150
200
Linear pressure (kN/m)

0250

Fig. 5 Smoothness increase by supercalendering for
A2 coat and uncoated woodfree papers

Amount of ink transferred (g/m 2 )4

Bekk smoothness (s)［Uncoated］

Bekk smoothness (s)［Coated］

2500

Bekk smoothness (s) ［Uncoated］
50
100
150

3.5
3
2.5
2
1.5
1
Coated 0.4cc
Uncoated 0.4cc

0.5Coated 0.2cc
Uncoated 0.2cc

0
0

500
1000 1500 2000 2500
Bekk smoothness (s) ［Coated］
Fig. 7 Ink transfer depending on
smoothness of paper

Quantifying

methodofamountofinktransferred by X-ray fluorescence analysis
Figure 8 shows that the proportional
relationship held between X-ray intensity of coppertransferred on paper for a short period of time. It isconsidered that this method can be applicable formeasuring the amount of some major color inks
including inorganic elements, i.e. Cl and Fe.

and amount of ink transferred, which had beenmeasured gravimetrically, irrespective of the kindComparison between X-ray fluorescence methodof printed papers. For each kind of paper used inand optical density measurement

this work, almost the same gradient values and highFigure 9 shows the changes of thecorrelation coefficients were derived as shown in

differences in optical density between printed andTable 1. These results suggest that the X-ray

unprinted surfaces as a function of the amount ofintensity of copper is not influenced by paper

ink on paper. The differences in optical density

whether the paper contains a large amount of

were not proportional to the amount of ink on paper

inorganic components or not, and therefore thismeasured by the X-ray fluorescence method.

method can be applied to most of the conventional

Lightness of the coated paper formulated withprinted papers. It follows that the amount ofhollow sphere pigment is high, since the large

cyan-ink printed can be determined by measuring

interface area provides high light scattering7,8). The

the X-ray intensity of copper in an X-ray

prints with coated paper with high lightness showed

fluorescence spectrum. Using this method, we canhigher optical density when the amounts of ink on

measurepaper were the same. Slight differences of the

preciselytheamountofcyan-ink

amount of ink, e.g. about 0.05 g/m2 , could not be

Copper X-ray intensity (cps/µA)

0.16measured by the differences of optical density. It

Woodfree
CoatedGroundwood
Recycled

0.14
0.12
0.1

has been reported that the print density was notproportional to the amount of ink transferred in thecase of the prints at relatively large ink amounts1)

0.08

and with some kinds of coatings 2). However, the

0.06

quantification method of the amount of ink

0.04

y = 0.0154x

0.02

R = 0.995

2transferred by X-ray fluorescence analysis is
0.68

0
1

2

3

4

5

6

7

8

9 10
2

Amount of ink transferred (g/m )Fig. 8 Calibration line for converting
X-ray intensity of copper to amount of ink

Table 1 Relationship between X-ray intensity ofcopper and amount of ink transferred
Kind of paper

Gradient

Correlation
coefficient

Woodfree0.01530.969

Coated

0.01520.900

Groundwood

0.0154

0.986

Recycled

0.01530.985

Difference in optical density :⊿D (%)

0

0.675
0.67
0.665

FilledHollow
Control

0.66
0.655
1.6

1.65
1.7
1.75
1.8
1.85
2
Amount of ink on paper (g/m )Fig. 9 Changes of optical density
vs. amount of ink on paperespecially suitable for measurement of the large

analysis. This is because the differences in ink

amount of ink transferred, and is applicable toamount between shadow and highlight parts were

almost all the prints.

very small at a low inking, and then sufficient X-ray
intensity was not obtained. Tables 2 and 3 show the
X-ray intensity of elements contained in the prints

Application for ink mottling analysis
Figure 10 shows the surface roughness ofmeasured

using

an

X-ray

fluorescence

unprinted parts of the poor print and the good print.

microanalyzer and FE-SEM/EDX, respectively. The

The surface roughness of unprinted parts of the

X-ray intensity of copper of the good print wasgood print was higher than that of the poor print inhigher than that of the poor print. These results

the wavelength range up to 300 µm. For the goodsuggest that all of the amounts of ink transferred ofprint, more concaves with about 10 µm diameter

the good print were higher than those of poor print.

were observed on the coated paper surfaces by

The X-ray intensity of calcium of the good print

SEM observation. It seems that these small

showed higher values than that of the poor print. On

concaves caused to increase the surface roughness.

the other hand, the X-ray intensity of aluminum andHowever, surface roughness of both prints showedsilicon of the good print showed lower values thanalmost the same values at about 250 µmthat of the poor print (Table 2). In the results ofwavelengths that were reported as affecting

FE-SEM/EDX, which provides surface analysis, theprintability. This suggests that surface roughness ofdifferences of the X-ray intensity between the goodbase paper do not affect mainly print mottling.

and poor print increased. These results indicate that

Figure 11 shows the results of mapping

calcium carbonate was rich at the parts close to theanalysis of copper and other elements like Ca, Al

coating surface of the good print and clay was richand Si of coating components contained in theat those of the poor print. For these reasons, it isprints measured using an X-ray fluorescence
theTable 2 X-ray intensity (cps) of elements contained

distribution of X-ray intensity of copper and thein prints measured by X-ray fluorescence

print mottle was not obtained from the mapping

microanalyzer

microanalyzer.

The

correlation

between

Cu-Kα

Ca-Kα

Al-Kα

Si-Kα

Poor print

0.558

8.98

2.52

4.52

Good print

0.566

10.0

1.53

3.21

Centerline average roughness
(µm)

1.60
1.40
1.20
1.00
0.80

Table 3 Ratio of X-ray intensity of elements

Poor
0.60

Good

contained

inprints

to

that

of

platinum

0.40

measured by FE-SEM/EDX
0.20

Cu/Pt

Ca/Pt

Al/Pt

Si/Pt

Poor print

0.062

9.91

18.71

18.18

Good print

0.074

22.97

11.15

12.43

0.00
0

200
400
Cut-off wavelength (µm)

600Fig. 10 Surface roughness of unprinted
parts of the coated papers

Cu-Kα , poor

Cu-Kα , good

Ca-Kα , poor

Ca-Kα , good

Al-Kα , poor

Al-Kα , good

Si-Kα , poor

Si-Kα , goodFig. 11 Mapping images of the X-ray intensity of elements contained in prints measured
using an X-ray fluorescence microanalyzer

indicated that when clay and/or binder is rich at the

The amount of ink transferred was found toparts close to the coating surface, the decreased rate

decrease with increasing smoothness of base paperof penetration of a dampening solution for printing

in the case of offset printing. As the amount of ink

results in ink mottling. From the results, it istransferred reflects the properties of paper, it issuggested that uneven distribution of coating

expected that the X-ray fluorescence based

pigments is one of the factors affecting ink

quantifying method of ink on paper assists inmottling.

estimating the printability of a variety of printing
papers.

CONCLUSION
The quantifying method of amounts of ink

ACKNOWLEDGMENT

transferred by X-ray fluorescence analysis was

The authors wish to thank Mr. Hiroyuki

established for offset printing with process cyan-ink.

Fukasawa, Fuji Industrial Research Institute ofIn this technique, the content of copper included in

Shizuoka and Ms. Yoko Saito, Nippon Zeon Co.,a cyan-ink printed on paper is evaluated from anLtd., for their help in the experiments. We are also

intensity of its peak in the X-ray fluorescencegrateful to Mr. Tatsuhide Tohara and Mr. Masanobu

spectrum.

held

Kawabata, EDAX Japan K.K., for their contribution

between the copper content so measured and thein the analysis using an X-ray fluorescenceamount of ink transferred, which had been

microanalyzer.

The

proportional

relationshipmeasured gravimetrically, irrespective of the kindof prints. Using the calibration line to convert the

REFERENCES

X-ray intensity of copper to the amount of ink
transferred, we can quantify precisely the unknown
amount of cyan-ink printed for a short period time.
This method is expected to apply to measuring theamount of some color inks including inorganic

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2. Lepoutre P., DeGrace J. H. and P. J. Mangin：
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3. Oshima S.： Japan Tappi 53 (5) 571 (1999)

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4. Publication

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5. Wakabayashi H.：Paper & Pulp No.600 20

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(1999)

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6. Lepoutre

especially effective for prints with rela tively large

CIE

P.

and

DeGraceJ.

H.：PaperTechnology and Industry 19 (9) 301 (1978)

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the elements contained in prints by the X-ray

ISWPC, Korea, 1999, pp309-314

fluorescence method, it is concluded that the
distribution of the coating components near thesurface affect the rate of penetration of a dampening
solution for printing, which leads to ink mottling.

8. Hamada H., Enomae T., Onabe F. and Saito Y.：

Japan Tappi 55 (11) 79 (2001)