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

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

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

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

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

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

A convenient 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.

References

1. M.Yamagami, T

and S.Nishida

2. M.Yamagami, T

and S.Nishida

3. S.Okabe, K.

I.Sakamoto, T

(1974)

314

.Ohnishi, M.Furuta,

, Chemistry Express,

.Ohnishi, M.Furuta,

, Proc. RadTech Asia

Tsumori, T.Tabata,

.Kawai, K.Arakawa, T.

H.Miyoshi, M

5, 809 (1990)

H.Miyoshi, M

'91, Conf. on

T.Yoshida,

Inoue, and T.

.Chubachi, T.Kitao, A.Kawata,

.Chubachi, T.Kitao, A.Kawata,

Radiation Curing, 1991, 534.

A.Nagai, S.Hiro, K.Ishida,

Murakami, Oyo Eutsuri, 43, 909