Process for fabricating display panel

A process for fabricating display panels in which which comprises printing one surface of a pulp paper with a plurality of printed image layers exactly overlaying and aligned with each other bonding; the image bearing surface of the pulp paper bonded to one surface of a panel base; and removing the pulp paper so that the display image is transferred to and remains on the panel base.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for fabricating in a simple 
manner display panels each of which can be displayed sharply and vividly 
and exhibits a higher degree of resistance against weathering. 
2. Description of the Prior Art 
In general, for the purpose of advertisement, many display panels having 
the same display pattern are fabricated at one time and in order to make 
them attractive, almost all of them use color photographs. In fabrication 
the photographic process has been widely used for printing a desired color 
picture or display image over the surfaces of panels, but the fabrication 
costs are high. In addition, such display panels are defective in that 
they are easily susceptible to weathering and consequently the color is 
faded therefrom. This fading effect is especially pronounced in display 
panels whose back is illuminated with a flood of light from fluorescent 
lamps or the like. Fading of display panels placed outdoor is very fast. 
Furthermore, glass or acrylic resin sheets are normally used as the base of 
display panels, and printing over the surfaces of these arcylic sheets is 
difficult so that high-quality display images cannot be reproduced. 
SUMMARY OF THE INVENTION 
One of the objects of the present invention is therefore to provide a 
process for fabricating display panels which exhibit satisfactorily high 
resistance against both weathering and color fading. 
Another object of the present invention is to provide a process for 
fabricating display panels which have sharply and vividly displayed images 
thereupon. 
A further object of the present invention is to provide a process for 
fabricating display panels by a minimum number of simplified steps. 
Briefly stated, to achieve the above and other ends, the present invention 
provides a process for fabricating display panels comprising reproducing 
over one surface of a sheet of pulp paper an image pattern consisting of a 
plurality of printed image layers exactly overlaid over and aligned with 
each other; a bonding step for bonding the ink-image bearing surface of 
the sheet of pulp paper to one surface of a panel base; and a pulp paper 
removal step for removing the sheet of pulp paper from the panel base so 
that the image pattern is transferred to and remains on the panel base. 
Since a display panel fabricated by the process of the present invention 
bears an ink printed display image, it can exhibit a higher degree of 
resistance against weathering and color fading as compared to those 
fabricated by the conventional photographic process. According to one 
aspect of the present invention, the display-image bearing surface of the 
panel base is coated with a protective layer or film of polyester which 
prevents the transmission of ultraviolet rays so that the resistance 
against weathering can be further improved. 
In addition, display panels fabricated according to the present invention 
can be vividly displayed in color and exhibit a higher degree of 
transparency as compared with those fabricated by the prior art 
photographic process. 
According to the present invention, a display image printed over the 
surface of a sheet of pulp paper consists of a plurality of printed image 
layers which are correctly overlaid over and aligned with each other so 
that the density, contrast and tone of the display image can be optimamlly 
controlled, even when a conventional printing process is employed. At the 
present time, because of relatively low trapping, it is difficult to 
transfer an ink layer greater than 0.01 mm over the surface of printing 
paper or the like. In the case of display of a single printed image layer 
display image by the transmission of light, satisfactory density, contrast 
and other characteristics cannot be attained. However, according to the 
present invention, a display pattern consists of a plurality of printed 
image layers which are exactly overlaid over and aligned with each other 
so that the display image can be increased in thickness and consequently 
the high-quality representation can be ensured. 
The process embodying the present invention can be automated in a simple 
manner and each fabrication step can be simplified because a printing 
process is employed. As a consequence, many display panels can be mass 
produced at less costs.

Same reference numerals are used to designate similar parts throughout the 
figures. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, first an image pattern in the form of an inked image 
layer; that is, a printed image layer 2 is reproduced over one surface of 
a sheet of pulp paper 1 by the conventional planographic printing or 
gravure process. In the case of four-color process printing, four printing 
plates are used to reproduce the printed image layer 2 so that the latter 
consists of four patterns of different colors. The pulp paper 1 bearing 
the printed image layer 2 per se can be used as a display or a poster. 
For the sake of clear and simple illustration, the surface of the printed 
image layer 2 is shown as being flat and uniform in thickness throughout 
the figures, but the thickness and the density of the printed image layer 
vary in practice. In the case of gravure process, the printed image layer 
2 consists of many multicolor ink columns of extremely small diameters. 
The same inked image is transferred over the printed image layer 2 in exact 
alignment therewith. To this end, the pulp paper 1 with the first printed 
image layer 2 is passed through the same printing press. In this case, 
even when an automatic feeding device is used, errors in misalignment 
between the first and second printed image layers are of the order of from 
a few tenths of one millimeter to a few hundredths of one millimeter. In 
the case of planographic printing, a small quantity of water is spread 
over the face of a printing plate so that printing paper is stretched to 
some extent. Therefore if a suitable time interval is selected between the 
first and second printing and a suitable humidity control is employed, the 
errors in alignment can be reduced to a negligible level. In cases of 
posters and window and showcase displayers which are large in size, such 
alignment or registration errors are almost negligible. 
By repeating the printing with the same printing plate, a printed image 
consisting of a plurality of exactly overlaid and aligned printed image 
layers 2 can be deposited as shown in FIG. 2 (where three printed image 
layers 2 are shown). 
Thereafter, as shown in FIG. 3, an adhesive 4 is uniformly applied over the 
image bearing surface of the pulp paper 1 or a surface of a transparent 
panel base 3 and the pulp paper 1 and the transparent panel base 3 are 
pressed against and securely joined to each other. The panel base 3 may be 
a sheet of acrylic resin or glass. In order to ensure uniform bond between 
the pulp paper 1 and the panel base 3, they may be passed between a pair 
of pressure rollers (not shown). Alternatively, a squeezer or the like can 
be applied to the nonprinting surface of the pulp paper 1 (on the right 
side in FIG. 3). It is preferable that the adhesive 4 exhibits chemical 
affinity to the ink on the pulp paper 1. For instance, it is preferable to 
use adhesives whose bases are vinyl resins. 
Next a dilute solution of caustic soda is applied to the nonprinting 
surface of the pulp paper 1 which is now bonded to the panel base 3. 
Alternatively, the bonded assembly; that is, the pulp paper 1 and the 
panel base 3, is immersed into a bath containing a dilute solution of 
caustic soda. After the pulp paper 1 is sufficiently softened, it is 
removed from the base 3 with a brush or the like while spraying water over 
the pulp paper 1 so that removed paper tissues can be washed away as 
slurry and consequently the removal step can be much facilitated. In 
general, the printing ink is water repellant so that the printed image 
layer 2 can be prevented from being washed away or degraded. 
With the pulp paper 1 is removed in the manner described above, a 
transparent positive image defined by the printed ink is left on the 
transparent panel base 3 as shown in FIG. 4. In some cases, the 
transparent positive image is not satisfactory from the viewpoint of 
transparency. The reason is as follows: When the print ink is deposited 
directly over the surface of pulp paper 1 and the adhesive 4 is applied 
thereto, they penetrate into the pulp paper 1 to some depth and bind some 
pulp filaments. As a result, even after the pulp paper 1 has been washed 
away, the bound pulp filaments remain over the exposed surface of the 
display pattern, giving rise to minute surface irregularities. As a 
consequence, the surface has a diffused or unclean appearance in respect 
to the display pattern, which degrades the display effects. In this case, 
a clear agent, such as transparent lacquer, can be applied to the image 
bearing surface of the panel base 3 so that the image becomes completely 
transparent. Thus, the panel base 3 becomes like an extremely large-sized 
color slide and the resolution of the image is sufficiently comparable 
with high-quality posters or displays. 
The display panel prepared in the manner described above can be used 
without any further processing, but according to another embodiment of the 
present invention, the image bearing surface of the display panel base 3 
is coated with a transparent plastic protective layer 5, thereby 
protecting the printed image layer 2 from damage. The protective coating 5 
is preferably white-milk in color and is made of a material exhibiting 
light diffusion when the display panel is used in combination with an 
illumination device without a diffusion plate. In this case, a flood of 
light from fluorescent lamps or the like can be projected directly over 
the back surface of the panel 3 so that light is transmitted through the 
display panel and consequently the display of the image can be enhanced. 
The display panel itself exhibits a high optical transmittance so that the 
image is by far brighter and clearer in color as compared with the case in 
which the back surface of a poster bearing an image printed by the 
conventional printing process is exposed to a flood of light for 
illumination. Especially areas in which the image has a metallic luster 
looks very vividly and real because of the transmission of light 
therethrough. 
On the other hand, the display panel with or without the transparent 
protective coating 5 of the present invention must be displayed by an 
illumination device of the type having a diffusion type lighting panel or 
the like upon which is placed the display panel so that light is 
transmitted the whole area thereof.