Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~IE INVENTION
Field of the Invention
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The present invention relates to a method of curing
photosensitive resin layers, and more particularly relates to
a method of curing photosensitive resin layers with the
ultraviolet light produced by a flash discharge lamp
Description of the Prior Art
Only a little over ten years have passed since attention
was first drawn to the photosensitive resins. Ho~ever, their
uses have been remarkably extended as a result of succeeding
developmental efforts, starting from the initial application
to photoengraving materlals and now including printing ink,
coating compositions, adhesives and other industrial product
They are used in the form of sheets, film, patterns, and
letter, and are cured from the liquid into the solid state
through irradiation of ultraviolet light. Chemically, this
process is photopolymerization of low molecular weight substances
induced by ultraviolet light, but is sometimes called "drylng"
in the paint and printing ink fields.
Conventionally a mercury discharge lamp, or a mixed-
metal-vapor discharge lamp, a modification of the mercury
discharge lamp in which part of the mercury is replaced by
other metals, has been used as the W-light source However,
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these lamps suf~er from the following disadvantages:
(1) It generally several minutes; several tens of
seconds even with the most advanced type; to generate the tQtal
amount of ~ight designed after starting the lamp. This results
in poor operation efficiency.
(2) It is known that, to overcone this difficulty, the
lamp is housed in a casing provided with a shutter and curing
is carried out by intermittent opening of the shutter. However,
the ccmplicated structure of the casing, its troublesome handling,
and unnecessary consumption of power are the disadvantages involved
in this method.
(3) In order to efficiently emit the light of the wave-
length region which is effective for photopolymerization, the
bulb wall must always be maintained at high temperatures to
ensure a high vapor pressure of the metal at all times. As a
result, the life of the bulb is liable to be shortO Also,
because of the large amount of heat produced, combined with the
longer irradiation time required, sharp reproduction of images
may be affected physically, or by a thermochemical reaction which
proceeds concurrently with the photochemical reaction, in the case
of letters and patterns which are composed of fine lines.
SUMMARY OF THE INVENTION
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The object of the present invention is to offer a novel
method of curing photosensitive resin layers which is free from
the disadvantages mentioned above The present invention
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relates to a method vf curing photosensitive resin layers
having the main photosensitive peak in the wavelength -region
not more than 4500A to form solid layers having a thickness
of 100 microns or less, by using a flash discharge lamp with its
glass bulb filled with a rare gas as the main component, the
emission energy J (joule) generated from said flash discharge
lamp being controlled within the range of
0.02 < J/S < 8
wherein S (cm2) denotes the area to be irradiated; and a method
of curing photosensitive resin layers having the main photo-
sensitive peak in the wavelength region not more than 4500A to
form solid layers having a thickness of more than 100 microns,-
by using a flash discharge lamp with its glass bulb filled with
a rare gas as the main component, the emission energy J (joule)
generated from said flash discharge lamp being controlled within
the range of
0.002 ~ J/Sd ~ 2
wherein S (cm2) denotes the area to be irrad.iated and d (micron~
stands for the thickness of the photosensitive resin layer
after curing.
In short, the present invention consists in using, as the
source of ultraviolet light, a flash discharge lamp which is a
cold light source capable of instantly producing the total
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designed amount of light, and in reasonably controlling the
emission energy of that flash discharge lamp. -
Flash discharge lamps have been used for various industrial
purposes. However, it was revealed that they can be used
successfully as a means of curing photosensitive resin-layers,
as offered in the present invention, only under specific con-
ditions, for which a detailed and comprehensive investigation
was needed. The present invention has been accomplished as a
result of this investigation.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view showing an apparatus for
the method of the present invention.
Fig. 2 is a schemativ view illustrating the configuration
of a flash discharge lamp ~lsed in the present invention and
the power supply circuit.
DESCRIPTION OF _HE PREFERRED EMBODIMENTS
Fig. 1 shows a preferred embodyment of the present
invention in which an ink layer 2 preinted on an acrylic plate 1
to a thickness of about 20 microns in cured by means of a flash
discharge lamp 4 with a mirror 3 equipped adjacent thereto.
Fig. 2 illustrates a preferred configuration of said flash
discharge lamp 4 and the power supply circuit connected thereto.
Numeral 3' shows the support frame for an internal reflective
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surface to efficiently guide the flash light to the articl~ -
being irradiated with a minimum of loss, numeral 5 is a glass
bulb, numeral 6 is a metal cap to seal both ends of the bulb
airtight~ numeral 7 is a cathode, numeral 8 is an anode,
L is the discharge distance, and D is the inside diameter of the
bulb. The power supply circuit to start the flash discharge
lamp 4 comprises high voltage generator HV connected through
charging resistor R, discharging capacitor C and trigger switch
SWs and trigger electrode 9 connected to said high voltage
generator ~V. If trigger switch SW is closed to apply a high
electric potential to the flash discharge lamp and to ionize
the gas filled in the bulb, the electric charge accumulated in
the discharging capacitor will be discharge, causing the lams to
emit flash light.
Ink 2 is an offset printing ink having the main photosen-
sitive peak in the wavelength region not more than 4500A, for
example, "Toka UV-Cure BF" (Toka Shikiso Kagaku Kogyo). This
ink anc be instantly cured by irradiation of ultraviolet light
from the fIash discharge lamp without any adverse thermal effect.
In an example, an ink layer coated over the area of S = lOcm x 20cm
to a thickness (d) of about 20 microns was instantly cured to
give satisfactory solid film when irradiated under the following
conditions: discharge distance L = 26cm, inside diameter of
bulb D = 0.8cm, xenon gas charge pressure = 200mmHg, emission
energy J = 800 joules (to give an energy radiation density Q of
20.4), and t = 3msec. A number of flash discharge lamps having
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different bulb diameters of at least 0.3cm and ~liff~rent
discharge distances of at least 3cm were fabricated, and their
glass bulbs were filled wlth xenon, other rare gases or a mixture
thereof. Similar experiments as above were conducted using
these lamps with dlfferent J values. It was demonstrated from
these experiments that, if the value J/S is less than 0.02, part
of the resin layer ls left uncured. If the value J/S is larger
than 8, on the other hand, degradation occurs on the surface of
the cured film The former trouble may be ascribed to insuf-
ficient do~e of ultraviolet light, while the latter may be con-
sidered to be a deteriorated surface appearance due to thermal
degradation often encountered in p astic materials. In any
event, satisfactory results can be achieved only within the
range of 0.02 ' J/S '- 8.
Other factors considered were the thickness of the ink
layer and the distance between the flash discharge lamp and the
ink layer. Experiments revealed that the thickness of the ink
layer has no effect on the result for levels not larger than 100
microns; the distance between the lamp and the ink layer was
found to have no effect within the range of 5cm to 25cm, if the
support frame is provided.
In another serles of experiments in which the value of
S x d, that is, the quantity or the volume of the ink present
on a given area, was varied, it was demonstrated that, if the
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value J/Sd is less than 0.002, part of the resin layer is lef~
uncured. If this value exceeds 2, on the other hand, degra-
dation occ~rs on the surface of the cured film. The former
trouble may be attributed to insufficient dose of ultraviolet
light, while the latter is considered to be a deteriorated
surface appearance due to themal degradation often encountered
in plastic materials. In this case, too, satisfactory results
can be achieved only within a definite range of dose, 0.002 -'
J/Sd ~ 2.
The effect of the amount of ink was investigated because
of the findings that curing is influenced by the thickness of
ink (which defines the amount of ink present on a given area)
when it exceeds 100 microns. It was found that the distance
between the lamp and the ink layer has no effect even for the
larger ink thicknesses.
As is apparent from the above, the present invention
relates to a method of curing photosensitive resin layers to
give satisfactory solid film free from disadvantages unavoidable
in conventional method, by using, as the source of ultraviolet
light, a flash discharge lamp which is a cold light source capable
of instantly producing the total designed amount of light and
by reasonably controlling the emission energy generated from
that flash dischage lamp, and is highly valuable in practical
applications.
