JPH09295484A - Sheet for protection against duplication and forgery and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely visualize a latent image in a duplicate, if the screen density of a background is decreased and the screen density of a latent image is decreased accordingly. SOLUTION: The halftone dot screen of at least either of a first pattern 3 and a second pattern 4 is constituted of a gathering of halftone dots P of an uneven size. In addition, the first pattern 3 is printed by a halftone dot screen plate with the number of lines selected arbitrarily from the range of 150-200 lines and the density from the range of 7-15%. Further, a second pattern is printed by a halftone dot screen plate consisting of a negative plate with the number of lines selected arbitrarily from the range of 50-80 lines and the density from the range of 15-25%, and a positive plate with the number of lines selected arbitrarily from the range of 25-35 lines and the density from the range of 30-50%, superposed at a specified angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copy forgery prevention sheet which makes it possible to determine whether or not a latent image appears on a copy made by a copying machine, and more specifically, a net having a new structure. The present invention relates to a copy forgery prevention sheet having a latent image or a background applied from a dot screen plate.

[0002]

2. Description of the Related Art Usually, when a sheet printed with a special screen plate is copied, a latent image (warning character) which cannot be seen on the actual sheet appears on the copy, so that it is a copy. In the hidden word method, which can discriminate whether or not, two kinds of screen plates having the same density with different line numbers are used, one of which is a latent image and the other is a background.
For example, if the background is 175 lines 20% and the latent image is 65 lines 20%, the background and the latent image cannot be distinguished with the naked eye in the actual sheet, but only the latent image appears in the copy, and in the copy. It can be determined that there is.

[0003]

In the conventional copying machine,
When a halftone screen having a screen density of about 20% was used, the background disappeared and the latent image remained, so that the latent image was sufficiently revealed in the copy. However,
In the recent copying machines, the background is revealed due to the improved resolution, and the background cannot be distinguished from the latent image in the copy. Therefore, in order to prevent the background from appearing, the screen density of the background is further lowered, and the screen density of the latent image is also lowered accordingly, but when the copy density adjustment of the copying machine is set low. Causes a problem that the latent image does not appear in the copy.

Therefore, according to the present invention, in the hidden word method which makes it possible to discriminate whether or not a latent image appears on a copy by a copying machine, it is possible to identify the background of the copying machine with improved resolution. It is an object of the present invention to provide a copy forgery prevention sheet that reliably reveals a latent image in a copy even if the screen density is lowered, and the latent image screen density is reduced accordingly, and a most efficient method for producing the sheet. To do.

[0005]

A conventional halftone dot screen is composed of a set of halftone dots of equal size and regularly arranged. Therefore, at the time of copying, all the halftone dots appear to the same degree or all the halftone dots disappear to the same degree. However, if the size of the halftone dots is made non-uniform (with this, the screen density also partially changes),
Large halftone dots are likely to appear and small halftone dots are likely to disappear.

For example, even if the copy preparation density is set to the lowest, it is assumed that halftone dots of 65% line 20% will appear. In the conventional method, in order to camouflage the latent image, the density of the halftone dot screen of 175 lines must also be 20%, but at 175 lines 20%, it appears when the copy preparation density is increased. As a result, the background and the latent image cannot be distinguished in the copy.

Therefore, for example, as shown in FIG. 3, a halftone dot screen plate of a latent image is added to halftone dots having 65 lines and 20%, and halftone dots having the same number of lines and having screen densities of 5, 10 and 15%. By dispersing halftone screens having different sizes and mixing them at an appropriate ratio, the average density of the whole latent image halftone screen can be reduced to about 10%. Moreover, even when the copy preparation concentration is the lowest,
Since 65% lines and 20% halftone dots are also present in the halftone screen at a specific ratio, a latent image appears on the copy.

Therefore, with such a configuration, for example, the density of the halftone dot screen of 175 lines in the background is also 10%.
By lowering it to a certain extent, it is possible to support recent copying machines with improved resolution, and therefore the latent image cannot be discerned with the naked eye on the actual sheet, but in the copy, only the latent image appears and It can be determined whether or not there is. However, it is difficult and costly to make a plate by specifying the sizes of halftone dots to be non-uniform.

Therefore, the present inventor has prepared a halftone dot screen plate in which the size of halftone dots is non-uniform by superposing the negative plate and the positive plate at a predetermined angle. That is, by superimposing the negative plate and the positive plate of a predetermined halftone screen at a predetermined angle, the halftone dots of the negative plate overlap the halftone dots of the positive plate, and the halftone dots of the negative plate are irregularly parted or not. All were in a defective state, and as a result, the average screen density as a whole was lowered, and a halftone dot screen plate having nonuniform halftone dot sizes was obtained.

Here, FIG. 1 is a schematic state explanatory view in which a negative plate and a positive plate of a halftone screen are superposed at a predetermined angle. As shown in FIG. When the negative plate A of 30% line and the positive plate B of 65% line are overlapped at an arbitrary angle θ, each halftone dot in the negative plate A has a missing part, so the area of the missing part And the halftone screen thus obtained has an average screen density of less than 30% as a whole. The present invention is based on this principle.

That is, in the copy forgery prevention sheet of the present invention, one of the latent image and the background is the first pattern and the other is the second pattern.
A copy forgery prevention sheet having a first pattern and a second pattern, which are difficult to discriminate with the naked eye and are formed by a halftone screen having a predetermined screen density on the surface of a sheet substrate, At least one of the halftone screens of the first pattern and the second pattern is constituted by a set of halftone dots of non-uniform size.

In the method for producing a copy forgery prevention sheet according to the present invention, the first pattern is printed with a halftone dot screen plate arbitrarily selected from the range of the number of lines of 150 to 200 and the density of 7 to 15%. And, the second pattern has 50 or more lines.
Negative plate arbitrarily selected from the range of 80 lines and density 15 to 25% and positive plate arbitrarily selected from the range of line number 25 to 35% and density 30 to 50% are overlapped with a predetermined overlapping angle. It is characterized in that it is printed with a halftone screen plate obtained together.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The copy forgery prevention sheet and the method for producing the same according to the present invention will be described below. Further details will be given based on a survey on halftone dot screen plates obtained by deleting all or part of the rules.

At present, the most commonly used combination of the halftone screen frequency of the background and latent image is the background 15
The latent image is about 50 to 80 lines with respect to 0 to 200 lines. Under these conditions, the halftone screen density should be 15% as a whole in order to cope with recent copying machines with improved resolution.
In order to make the latent image appear in good condition when the copy adjustment density is set to the lowest, the latent image may vary depending on the screen color. There is at least about 18% halftone dots in the halftone dot screen, and it is better to have as many as possible.

Based on these conditions, first, for a given negative plate, what is the overall halftone dot screen density of the latent image obtained by changing the screen ruling and density of the positive plate and the superposition angle. I investigated whether it would change to. Specifically, 65 lines 20 on the halftone screen of the negative plate
%, Using various positive plates with different screen rulings and densities, each with a stacking angle of 5 to 75
The average screen density of the obtained halftone screen plate was investigated by superimposing it in steps of 10 degrees in the range of degrees. Table 1 shows the obtained survey results.

[0016]

[Table 1]

As a result of the investigation, it is absolutely necessary to have a predetermined angle so that the halftone dots of the halftone dot screen forming the latent image are irregularly different in size from each other. However, it was found that the density of the halftone screen as a whole was not so much influenced by the superposition angle of the negative plate and the positive plate, but was greatly influenced by the number of lines and the density of the halftone screen.

Then, the halftone dot screen of the negative plate is set to 65 lines 20%, the stacking angle is fixed to 30 degrees, and the halftone dot screen densities of the positive plate are 30% and 40%.
It was investigated how the halftone screen density distribution of the latent image obtained by changing the screen ruling of the positive plate and the average value of the overall screen density change. The results of the investigations are shown in Table 2 for a halftone screen density of 30% for a positive plate and in Table 3 for a halftone screen density of 40%, respectively.

[0019]

[Table 2]

[0020]

[Table 3]

As a result of the above investigation, the density distribution of the halftone dot screen caused by the change of the halftone dot area due to the irregular or partial loss of the halftone dots greatly changes depending on the number of lines of the positive plate. There was found. That is, when the number of lines of the positive plate to be superimposed on the halftone dots of the negative plate (65 lines) is larger than that of the negative plate, the area of each halftone dot becomes almost uniform, and a peak exists near 11%. Further, when the number of lines of the positive plate was made to be about the same as that of the negative plate, the peak became gentle and the distribution of halftone dot areas was dispersed. Further, it was found that when the number of lines of the positive plate was made smaller than that of the negative plate, the peak was shifted to the larger halftone dot area as it was made smaller.

Therefore, as a preferred example of the copy forgery prevention sheet of the present invention, for example, the background halftone dot screen has a line number of 175 lines and a density of 14%, and the latent image halftone screen has a negative plate of 65 lines 20. % And positive version 30 lines 40%
If is applied with a halftone dot screen plate obtained by superimposing and with a superimposing angle of 30 degrees, the average density of the halftone dot screen of the latent image can be reduced to about 14%, and
The existence rate of halftone dots having a density of 18% or more is 75% or more, and a latent image can be satisfactorily displayed.

The present invention will now be described in more detail with reference to the preferred embodiments of the copy forgery prevention sheet of the present invention.
2 is a schematic explanatory view of a copy forgery prevention sheet which is one embodiment of the present invention. The copy forgery prevention sheet 1 in this embodiment has a latent image on the surface of a copy. A "copy" is displayed. The cyan printing color is used on the two surfaces of the sheet base material, and the halftone dot screen frequency is 175 lines and the density is 1
The first pattern 3 (background) consisting of 4% and the halftone screen are made up of the negative plate 65 lines 20% and the positive plate 30 lines 40% 3
It has a second pattern 4 (latent image) which is a latent image printed by a halftone dot screen plate obtained by superimposing it at an overlapping angle of 0 degree.

As shown in the accompanying enlarged view, the halftone dot screen constituting the second pattern 4 has an average density of about 14% and is composed of a set of halftone dots P of non-uniform size. In the screen, about 75% of halftone dots of 65 lines are also present. The copy forgery prevention sheet 1 having a background and a latent image with such a configuration can be used to copy a copy by changing the copy density adjustment stepwise by using a commercially available copy machine (Canon PIXEL 700 and XEROX A-COLOR 935). When obtained, a latent image was well expressed in all the ranges of the copy density adjustment in any model.

[0025]

As described above, according to the copy forgery prevention sheet and the method for producing the same of the present invention, it is assumed that the overall halftone dot screen density is lowered corresponding to the recent copying machine with improved resolution. However, there is no inconvenience that a latent image does not appear in a copy as in the conventional case. Also,
It has the effect of efficiently applying such a special halftone screen version.

[Brief description of drawings]

FIG. 1 is a schematic state explanatory view in which a negative plate and a positive plate of a halftone screen are superposed at a predetermined angle.

FIG. 2 is a schematic explanatory diagram of a copy forgery prevention sheet that is an embodiment of the present invention.

FIG. 3 is a schematic state explanatory view of a halftone dot screen configured by dispersing halftone dots having different sizes and mixing them at an appropriate ratio.

[Explanation of symbols]

 1 copy forgery prevention sheet 2 sheet base material 3 first pattern 4 second pattern P halftone dot A negative plate B positive plate

Claims (2)

[Claims] 1. A copy forgery prevention sheet comprising a first pattern and a second pattern, which are difficult to distinguish with the naked eye, and which consist of a halftone screen having a predetermined screen density on the surface of a sheet base material. And at least one halftone screen of the second pattern is constituted by a set of halftone dots of non-uniform size. 2. The first pattern has a number of lines of 150 to 200,
Printed on a halftone dot screen plate arbitrarily selected from a density range of 7 to 15%, and the second pattern has 50 lines.
~ 80 lines, negative plate arbitrarily selected from the range of density 15 to 25% and positive plate arbitrarily selected from the range of line number 25 to 35%, density 30 to 50% with a predetermined overlapping angle The method for producing a copy forgery prevention sheet according to claim 1, wherein the sheets are printed with a halftone dot screen plate obtained by overlapping.