This document summarizes the development of a radiation indicator ink that changes color based on absorbed radiation dose. The ink was developed to allow quick and simple assessment of radiation doses used for sterilizing medical supplies. It contains diethylaminoazobenzene, which changes the ink color from yellow to orange, red, and purple as the radiation dose increases from 10 to 50 kGy. Testing found the ink color change corresponds directly to radiation dose, regardless of dose rate from 1.41 to 33.4 kGy/h. Electron beam irradiation also produced consistent results. The ink provides a convenient way to check sterilization doses for large quantities of supplies.

1. Journal of Photopolymer Science and Technology
Volume 5, Number 2(1992) 309 - 314
RADIATION INDICATOR INK
1. PHOTOGRAVURE INK
Masayuki YAMAGAMI,Akira KAWATA+,Set suo NISHIDA+, Akira HANAOKA+,
Tokuhiro OHNISHI, Masakazu FURUTA, Hirofumi MIYOSHI, and Mitsuo CHUBACHI
Research Institute for Advanced Science and Technology,
University of Osaka Prefecture, 1-2, Gakuen-cho, Sakai, Osaka 593, Japan
+ Koyo Chemicals Inc., 2-3-5, Norinomiya, Jyoto-ku, Osaka 536, Japan
we recently developed a radiation indicator using a photogravure
ink. This indicator allows simple assessment of absorbed doses of
7 -rays used for sterilization of medical supplies and absorbed doses
of 7 -rays and electron beams emploied in various kinds of industrial
fields. This indicator was prepared by coating the packing paper with
an indicator ink made primarily of diethylaminoazobenzene. When 7 -
rays were irradiated onto this indicator at a dose rate of 25.7 kGy/h,
a color of the indicator changed in proportion to the strength of a
dose and was well reproducible. Prior to irradiation, the color of
the indicator was yellow. This color changed to orange from yellow at
an absorbed dose of 10 kGy, to red at 25 kGy (a dose used for sterili-
zation) and to purplish red at 50 kGy. Within dose rate ranges of
1.41-' 33.4 kGy/h, the color was changed in proportional to only
absorbed doses as independent of the dose rate. The dose-response
curve of the indicator for electron beam irradiation which was
generated by a linear electron accelerator is in good agreement with
that for 7 -ray irradiation.
Received April 7 , 1992
Accepted May I1, 1992 309

2. J. Photopolym. Sci. Technol., Vol.5, No.2,1992
1. Introduction
For determination of absorbed doses in radiation sterilization of medical
supplies or in physical and chemical utilization of radiation, a variety of
indicators which can be symply measured absorbed doses have been commercialized.
In previous papers [1,2], the authors reported the method of manufacturing and
using a label-formed color indicator designed for checking absorbed doses
emploied for y -ray sterilization of medical supplies. The supply and demand
of medical supplies have been increasing in recent years. In respect of this
trend, a more efficient method of sterilization of medical supplies is now
required.
To satisfy such a jemand, we attempted to develop a radiation indicator ink
instead of a label-shaped indicator which consumed a lot of time for attaching
the label. If an indicator ink is printed directly onto the packing material
or the label of medical supplies, absorbed doses on large quantities of medical
supplies can be checked in a short period of time. In addition, the thus-
prepared indicator is less likely to become detached from medical supplies,
compared with the conventional label-formed indicator. This paper will present
the manufacturing method and the features of this radiation indicator ink for
photogravure printing.
The principle of color-changing at this indicator is shown in the equation 1.
When the indicator is exposed to radiation, hydrogen chloride is released from
polyvinyl chloride. Hydrogen chloride reacts with diethylaminoazobenzene (an
acid-sensitive dye), resulting in a change of the indicator color from yellw to
red.
2. Method
By using a
(commonly used
aminoazobenzene
ratio 9:1, 20.0
cyclohexane ( 2
bar coater ( No.
for sterilization)
(0.7 % by weight)
?), methyl ethyl
.8 %), chlorinated
10, Osaka Richo Co., Ltd.), a packing paper
was coated with a solution containing diethyl-
, vinyl chloride-vinyl acetate copolymer (molar
ketone ( 58.0 %), toluene ( 5.1 %), hexachloro-
paraffin ( Enpara-70, Sanko Inc., 13.3 %), and
310

3. J. Photopolym. Sci. Technol.,Vol.5, No.2, 1992
an antioxidant ( AD-51, Sakai Chem. Ind. Co., Ltd., 0.1 %). The paper was then
dried at room temperature for 10 minutes and was cut into size of 1.5cm x 2cm
test pieces. The thickness of the indicator ink was 3--6 u m when the paper was
dried.
Various kinds of dose rates of y -rays using 60Co sources were irradiated
onto the test pieces at room temperature for prescribed periods. Table 1 shows
the values of Curie numbers and the dose rates at the center of the basket of
the 60Co sources used in the present study. A standard absorbed dose of y -ray
irradiation in this study was determined by using an ionization chamber (Oyo
Giken Co., Ltd.)
Electron beam irradiation
was carried out at room temper-
ature, using a linear electron
accelerator (Highvoltage Engi-
neering Co., Ltd., U.S.A.).
The absorbed dose in electron
beam irradiation were
calculated by the equation of
Okabe et al.[3] (Equation 2).
Where 10, S and Y denote
electron-beam current, con-
veyer speed and irradiation
width, respectively.
Using a color densitometer
KRD-2100 (Ihara Electric Co.,
Ltd.) which is complied with
the ANSI ( American National
Standard for Photography), the
color of the indicator was
resolved into four components,
i.e., magenta (red), cyan
(blue), yellow and visual
(lightness), and the density
of each component was determined.
Table 1. 60Co sources.
311

4. J. Photopolym. Sci. Technol., Vol.5, No.2, 1992
3. Results and Discussion
The color of the indicator ink is a bright yellow before irradiation. The
amounts of diethylaminoazobenzene were adjusted so that the indicator ink
changed to red at an absorbed dose of 25 kGy (a standard dose used for y -ray
sterilization of medical supplies, see 2. Method). Table 2 shows the relation
between the color of the indicator and 7 -ray irradiation. The yellow color
of the non-irradiated indicator was increasingly tinged with red as the dose
increased, and the color changed red at a dose of 25 kGy.
After resolving the hue of the
indicator into four components, i.e.,
magenta (red), cyan (blue), yellow
and visual (lightness), we measured
the density of each color component.
Figure 1 shows a relationship between
the color density and the absorbed
dose. The density of the yellow
component gradually decreased as the
dose exceeded about 25 kGy. On the
other hand, the density of the red
component increased linearly in a
dose range between 5 and 50 kGy.
These results indicate that this
indicator ink can be utilized to
check the absorbed irradiation doses
between 5 and 50 kGy that are used
for sterilization.
Table 2. Color change of the indicator ink by 7 -ray irradiatione ) .
Fig.l Relation between the color
density and the 7 -ray irradiation
dose with dose rate of 25.7 kGy/h.
312

5. J. Photopolym. Sci. Technol., Vol.5,No.2, 1992
Figure 2 shows the relationship between the density of the red component
and the absorbed doses of 7 -ray generated from 5 sources with different dose
rates as shown in Table 1. (see 2. Method). In this Figure, all plots at
different dose rates lay approximately on a single curve. Therefore, in a dose
rate range from 1.41 to 33.4 kGy/h, the red density is proportional only to the
absorbed dose, regardless of the dose rate.
In Figure 3, the density of the red color by electron beam irradiation, used
a linear electron accelerator compares with that by y -ray irradiation. The
values of the color density by electron beam irradiation are in good agreement
with those by -ray irradiation. This result indicates that this indicator ink
can also be used to verify the measurement of electron doses.
Figure 4 shows the relation between the time and the density of the red color
of indicators stored in a dark place at room temperature. The non-irradiated
Fig.2 Plot of color density of the
indicator against 7 -ray irradiated
dose with various kinds of dose rates.
(L~:1.41, V:4.21, 0:8.52, []:25.7,
0 : 33.4 kGy/h).
Fig.3 Coloration of the indicator by y -
ray irradiation(0 :dose rate 25.7 kGy/h)
and electron beam-irradiation (d :energy
10 Mev, beam current 15^ 50 u A, irradi-
ation width 20 cm,conveyer speed 30 cm/min).
313

6. indicators
(below 10
storage.
decreased
indicator
J. Photopolym. Sci. Technol., Vol.5, No.2, 1992
and the indicators exposed to relatively low
kGy) showed hardly any change in the red density
The density of the red color in indicators by 25 kGy
5 % or less during a 50-day storage. Thus, fading of
with time was found to be negligible.
dose irradiation
during a 50-day
dose irradiation
the color of the
4. Conclusion
Aconvenient radiation indicator ink to check the doses of radiation was
developed for radiation sterilization. The indicator was prepared by coating or
printing the packing paper with the indicator ink made primarily of diethyl-
aminoazobenzen. The color of the indicator changes from yellow to red at 25 kGy
which is the optimum dose for y -ray sterilization. This new indicator is supe-
rior to the conventional label-formed indicators because the former indicator
is very shorter time to attach labels than the latter one. This indicator was
also found to be useful for determining absorbed doses of electron beams.
Fig.4 Discoloration test of the y -ray irradiated indicator.
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and S.Nishida
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I.Sakamoto, T
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