Method for manufacturing rotary screen

A method of manufacturing a rotary halftone screen which has no slit or meshless portion by the use of galvano process including a step of exposing the roll coated with high-sensitivity photosensitive film by a multiple number of laser beams. The multiple number of laser beams are controlled by preset electric data so that desired halftone points of negative halftone image are exposed on the roll.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of manufacturing a rotary screen 
and specifically to a rotary screen manufacturing method using a galvano 
process by which a rotary halftone screen with no slit or meshless portion 
is obtained. 
2. Prior Art 
FIG. 3(a) shows a conventional rotary halftone screen which is made of 
nickel and approximately 1 mm in thickness. The rotary halftone screen S 
has halftone meshes and a linear meshless portion G that is 0.2 to 0.3 mm 
in width and extends along the entire length of the halftone screen 
surface. 
As shown in FIG. 3(b) and 3(c), the shape of the halftone meshes is, for 
example, a regular hexagonal (a) or a regular square (b), and the halftone 
meshes are arranged in regular rows. 
When a printing is performed, ink is supplied from the inside of the rotary 
halftone screen S to the outer surface of the rotary halftone screen by 
wiping the inside surface of the rotary halftone screen S with an internal 
doctor so that ink is squeezed out through the meshes. The number of the 
rows of the halftone meshes is generally 60, 80, 100 or 120 per inch. 
In manufacturing rotary halftone screens, there are a lacquer method, a 
galvano method and an etching method. Among these methods, the galvano 
method will be described with reference to FIGS. 3(d) through 4(e). 
First, as shown in FIG. 3(d), a roll 1, which has surface properties that 
allow easy stripping of a nickel plating, is coated with a photosensitive 
film 2. A photo resist film 3 is laid over the photosensitive film 2, and 
the photosensitive film 2 is exposed by a UV light source 4. As a result, 
a negative halftone image 5 is made on the roll 1 as shown in FIG. 3(e). 
Afterward, the roll is plated by nickel so that the nickel 6 is filled in 
grooves of the halftone image as shown in FIG. 3(f). 
The halftone meshes are made by the process described above, and in order 
to obtain the rotary halftone meshes, following steps are taken. 
First, as shown in FIG. 4(a), the roll 1, that is coated with a 
photosensitive film, is held by a pair of chucks 7 of an exposure 
apparatus, and one end of the photo resist film 3 is fastened on the 
surface of the roll 1 by a transparent adhesive tape 8. Afterward, a first 
masking tape is fastened on the transparent adhesive tape 8 and the roll 1 
so that the edge of the first masking tape 9 is accurately aligned with 
the edge of the photo resist film 3. 
Next, as shown in FIG. 4(b), the second stage of the exposure process is 
performed. After the masking tape 9 is positioned under the UV light 
source 4, the LrV light source 4 is turned on, and the roll 1 is rotated 
in the direction indicated by arrow X. An exposure treatment is thus 
started. 
FIG. 4(c) illustrates the third stage of the exposure process. After a 
prescribed period of time has elapsed, the UV light source is turned off, 
and a second masking tape 10 is carefully applied so that the edge of the 
second masking tape 10 is overlapped 0.2 to 0.3 mm from the edge of the 
masking tape 9. 
FIG. 4(d) illustrates the fourth stage of the exposure process. After the 
second masking tape 10 is applied, the first masking tape 9 is stripped 
away, and the other end of the photo resist film 3 is fastened by an 
adhesive tape 11 on the second masking tape 10. 
After the photosensitive film is rounded on the entire surface of the roll 
1, the UV light source is turned on and the roll is rotated in the 
direction indicated by arrow X until the second masking tape 10 is 
positioned under the UV light source 4 as shown in FIG. 4(e). Then, the UV 
light source is turned off, and the exposure treatment is thus completed. 
In the conventional method of manufacturing rotary screens using a galvano 
process as described above, it is necessary to provide a 0.2 to 0.3 mm 
overlap of the second masking tape 10 over the first masking tapes 9 so as 
to make the rotary halftone screen. If the overlap is not provided between 
the two masking tapes 9 and 10, the both ends of the photo resist film 3 
are overlapped as shown in FIG. 5(b). Therefore, a groove on the 
photosensitive film cannot be formed between the both ends of the photo 
resist film. In other words, the grooves that are filled with the nickel 
plating are not formed along the entire length of the roll 1. As a result, 
rents C are formed in places along the entire length of the halftone 
screen is not formed as a round shape. 
On the other hand, the rotary halftone screen made by the conventional 
method has a meshless portion that corresponds to the gap as shown in FIG. 
5(a). Accordingly, it is impossible to print continuous patterns since ink 
is not supplied from the meshless portion. If it is desired to print 
continuous patterns, the holes (a) positioned along the meshless portion 
is retouched by skilled workers so as to enlarge the holes (a). 
Therefore, to make the rotary halftone screen used for continuous printing 
patterns requires considerable time and labor. 
SUMMARY OF THE INVENTION 
Accordingly, the object of the present invention is to provide a method of 
manufacturing rotary screens using a galvano process which forms a rotary 
screen with no meshless portion by a simple operation. 
In order to achieve the object, the present invention uses a unique method 
of manufacturing rotary screens in which (a) a roll coated with a 
high-sensitivity photosensitive film is supported at the both ends to 
undergo a rotary scanning motion, (b) a multiple number of laser beams 
arranged in a prescribed manner are caused to scan the length of the roll 
surface while the laser beams are intermittently driven on the basis of 
electronic data representing a desired halftone image, so that halftone 
points of the halftone image are subjected to an endless laser exposure by 
the laser beams, (c) a negative halftone image in which the halftone 
points remain is formed by subsequent development, (d) the other areas 
surrounding the negative halftone image portions are filled with nickel by 
a nickel plating process, and (e) the rotary halftone screen is peeled off 
from the roll.

DETAILED DESCRIPTION OF THE INVENTION 
An embodiment of the method of the present invention for manufacturing 
rotary screens will be described with reference to FIG. 1, FIG. 2(a) and 
2(b). 
First, a high-sensitivity photosensitive agent (polymer), which reacts to 
an argon ion laser with a wavelength of 488 nanometers, is coated on a 
roll 1 so that the photosensitive agent is formed with a uniform 
thickness. The roll 1 has surface properties in which a nickel plating can 
easily be peeled off from the roll 1. Thus, the roll 1 is, for example, a 
stainless steel roll, a nickel roll with an oxide coating, or a cooper 
roll with an organic film. 
After the photosensitive agent is dried, a transparent protective film, for 
example, polyvinyl alcohol, is coated on the photosensitive agent so as to 
prevent the photosensitive film from being oxidized since the 
photosensitive film tends to be easily oxidized and the photosensitive 
film loses its photosensitivity when the photosensitive film is oxidized. 
Next, as shown in FIG. 1, the roll 1 is held at both ends by chucks 12 
installed on a laser exposure apparatus, and the roll 1 is rotated in the 
direction indicated by arrow X. Afterward, a plurality of argon ion laser 
beams R with a wavelength of 488 nanometers, that are arranged in a 
straight chain arrangement, are emitted from a laser head 13 of the laser 
exposure apparatus to the surface of the roll 1, and the laser head 13 is 
scanned in the direction indicated by arrow Y. An emission of the argon 
ion laser beams R is controlled by electronic data for making a desired 
halftone image. As a result, the roll 1 is exposed by the argon ion laser 
such that regular hexagonal halftone points P are formed in a regular row 
and in spiral pattern on the surface of the roll 1 as shown in FIG. 2(a). 
In addition, the electronic data for controlling the emission of the argon 
ion laser beams R is predetermined in view of the circumference of the 
roll 1 and the size of the hexagonal halftone points P so that the regular 
hexagonal halftone points P are formed evenly for the entire surface of 
the roll 1. 
Next, the roll 1 is removed from the chuck 12, and the roll 1 is immersed 
and rotated in a developing solution. As a result, the negative halftone 
image in which the halftone points P remain is developed as shown in FIG. 
3(e), and the roll 1 is taken out from the developing solution. 
Afterward, the roll 1 is immersed and rotated in a nickel plating solution, 
and an electric current is applied to the roll 1 while the roll 1 is 
rotated in the nickel plating solution. As a result, the nickel 6 is 
filled in the negative halftone images 5, and the rotary halftone screen 
made of nickel is formed as shown in FIG. 2(b). 
After the roll 1 is taken out from the nickel plating solution, the roll 1 
is held at both ends and rotated at a low speed, and the roll 1 is pressed 
by a soft material, so that a pressure of the soft material against the 
roll 1 is applied to the nickel plating in the circumferential direction. 
Therefore, the circumferential length of the nickel plating is slightly 
increased so that the nickel plating can easily be removed from the roll 
1. The rotary screen is thus obtained. 
As described above, the method of the present invention of manufacturing 
rotary screens is a method of manufacturing rotary screens using a galvano 
process which is designed so that an endless laser exposure is performed, 
thus making it possible to obtain a negative halftone image in which the 
halftone points are arranged in spiral oblique rows or straight rows. 
Accordingly, the fatal drawback of splitting of the pattern by a white 
line is eliminated. Furthermore, the exposure process is greatly 
simplified, and there are no errors resulting in the generation of rents 
in the screen.