JPS6345316B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for performing multicolor wet overlapping printing on the surface of a printing medium by an offset printing method.

There are various types of printing materials on which multicolor printing is desired, such as flyers and pamphlets for advertising, and the surfaces of packaging containers. One of these, the metal can, is made by printing multicolors on a flat rectangular metal material using an offset printing machine, then cutting the metal material into the size of one can and forming it into a can. Three-piece can and
There are two-piece cans in which a cylindrical can body with a bottom is first formed and then multicolor printing is applied to the can body using an offset printing machine. In the color printing method, dry baking is performed after each printing of one color by one printing machine or two colors by two printing machines, so in the case of the most common four-color printing. requires four or two dry baking steps.

This method allows multi-color overprinting, so it is possible to print extremely close to the original image, but on the other hand, it requires four or two dry-baking steps, and also requires a cooling period between dry-baking and the next printing. Therefore, there are disadvantages in that it takes a long time for printing as a whole and a large amount of heat is consumed for drying and baking the printing ink.

On the other hand, in the case of printing two-piece cans, since the printing material is cylindrical, after printing and drying,
If we decided to print again, it would be difficult to align the printed surfaces during subsequent printing, so we use a single offset printing machine to print in multiple colors. That is, in a known method for performing multicolor printing, for example, four-color printing, on a two-piece can, first, four color ink images are sequentially transferred to the same position on the blanket surface from four printing plates arranged around the blanket cylinder, and then The transferred image is retransferred onto the surface of the can body, which is fitted into a mandrel of a rotating disc, contacts the blanket, and rotates as the blanket cylinder rotates, thereby producing a desired print on the surface of the can body.

In this known printing method, after printing in four colors, drying and baking of the four colors of printing ink is performed at once, so the printing time is shorter than in the case of three-piece cans, which are printed in multiple colors when they are flat. Although this method has the advantage that the amount of heat consumed by the drying and baking oven for printing ink is small, it has the disadvantage that multicolor wet overlapping printing is not possible.

In other words, in this printing method, when there is a part where the designs transferred from the plate surface to the blanket surface overlap, in that part, the wet inks pull each other and mix, changing to a completely different hue (the difference between each ink). If the tack values are almost the same),
Or, is the ink not being transferred from the printing plate to the blanket surface? (There is a considerable difference in the tack value of the ink on each printing plate that should be transferred from the printing plate to the blanket surface, and the tack value of the ink that should be transferred later is transferred first.) transfer from the plate surface to the blanket surface but not from the blanket surface to the can body surface (transfer from the plate surface to the blanket surface). (When there is a considerable difference in the tack value of the inks to be transferred, and the tack value is the highest for the ink to be transferred first and decreases from the ink to be transferred next) You end up becoming one of the following.

Let me explain the reason. Considering the transfer from the printing plate to the blanket surface, the first ink transferred from the first printing plate to the blanket surface has a high tack value, and then the first ink transferred from the second printing plate to the blanket surface has a high tack value. If the second ink to be transferred has a sufficiently lower tack value than the first ink, when the second plate surface and the blanket surface come into contact, the second ink will be transferred to the blanket even in the overlapping part of the ink. If the second ink has a larger tack value than the first ink, then when the second plate side and the blanket surface come into contact, the second ink will transfer well to the blanket surface in the overlapping area. Instead, the first ink on the blanket surface transfers to the second printing surface.
No transcription takes place. That is, in areas where inks overlap, a condition for good transfer is that the ink applied on top has a lower tack value. This also applies to the case where the overlapping portions are three or more colors.

Next, considering the transfer from the blanket surface to the can barrel surface, we need to have good transfer conditions from the plate surface to the blanket surface (the tack value of the second ink in the upper layer is higher than the tack value of the first ink in the lower layer on the blanket surface). When the can body surface contacts the blanket surface, the film of the second ink, which has a lower tack value, splits in the area where both the first and second inks overlap, and the second ink Since only the ink is transferred to the can barrel surface and the first ink remains on the blanket surface, good transfer is not achieved.

Therefore, the condition for transfer from the blanket surface to the can body surface is that the lowest layer of ink in the overlapping portion of ink on the blanket surface has the lowest tack value, and then the higher the layer, the higher the value. That is, the tack value of each ink is, when four color inks are used, and if the first, second, third, and fourth inks are used from the bottom layer to the top layer of the blanket surface, then the first ink < the second ink < 3rd ink < 4th
It has to be related to ink.

However, this condition contradicts the above-mentioned transfer condition from the plate surface to the blanket surface. Therefore, the above-mentioned known printing method cannot perform multicolor wet overlapping printing.

The overlapping printing method is an essential printing method for reproducing the delicate and complex colors, shadows, gloss, etc. of actual articles, but its inability to use it is a major disadvantage in terms of design.

The applicant has discovered that when ink is transferred from the plate surface to the blanket surface, the wet ink on each plate surface is transferred onto the blanket surface. Can body multicolor printing is performed on cylindrical objects such as two-piece cans by overlapping each ink in descending order of tack value when transferring from the blanket surface to the can body surface, avoiding overlapping. We have developed a printing method and have already applied for it (patent application filed in 1972).
149008, Special Publication No. 62-58313).

In contrast, the present invention has been developed as a means that can be applied not only to the above-described multicolor printing method on can barrels, but also to a multicolor wet overlapping printing method on flat printing materials.

Before entering into the description of the present invention, an example of a multicolor wet overlapping printing method on a flat printing material to which the present invention is applied will be explained.

First, a plurality of traditionally used one-color offset printing machines are arranged in series, and the highest ink is selected as the first ink (i.e., the ink that is the lowest layer when viewed from above the surface of the printing material) of the printing machine that prints first. The tack value is used for the first printing, and then as the second ink (i.e., the ink on top of the first ink on the surface of the printing material) of the next printing press,
A second printing is performed using an ink having a lower tack value than the first ink, and a third printing is performed using a third ink having a tack value lower than the second ink. A fourth printing is performed with a fourth ink having a lower tack value, and then the substrate is sent to a drying and baking oven for drying and baking these four printing inks at once.

During the above-described printing, since the positioning of the printing material in each printing machine can be performed accurately using the corners of the printing material, the printed image will not be misaligned due to each ink.

According to this method, the drying and baking process is performed only once, so the overall printing time is shorter than in the conventional method, and the amount of heat consumed for drying and baking is also smaller.

In the above example, wet overlapping printing is performed using four colors, but it can be similarly performed using two colors, three colors, or five or more colors.

Using this method, multicolor printing of three or more colors can be achieved by going through the steps of wet overlapping printing of two or more colors → dry baking → wet overlapping printing of two or more colors (or overlapping printing of one color) → dry baking. Of course, it is also possible to do so.

In order to perform multicolor wet overprinting on a cylindrical or flat article using this method, for the reasons mentioned above, the ink that forms the lowest layer on the surface of the printing medium has the highest tack value, and the next Each ink in the layer must be adjusted to have a lower tack value in order, but the inventors have found that the known method for adjusting the tack value of ink has the following problems. In other words, as a means of adding tack to ink, methods by adding reducers or compounds have been known up to now, but when these methods are used, the ink's flowability (fluidity), color density, etc. This means that the characteristics will change.

When the flowability of the ink increases, the lines (characters, halftone dots, etc.) become more likely to collapse, resulting in a decrease in sharpness. Parts become matte and the appearance deteriorates. Furthermore, if the color density decreases, more ink must be applied to compensate for this decrease, which also makes the image lines more likely to collapse.

In particular, if a large amount of the above additives is used, it will greatly affect printing suitability, such as running lines and poor wet clear suitability (ink bleeds), and the print finish will also suffer from sharpness of letters, etc. The quality may be poor, or the color reproducibility (finishing in the same color as the original) may be poor, resulting in quality problems.

Therefore, it is an object of the present invention to provide a printing method that allows good multicolor wet overprinting by giving different tack to each ink without affecting properties other than the tack of the ink as much as possible. do.

As a result of research, the present inventors have found that the tack value and flow value of ink change as the temperature changes;
We obtained the knowledge that the degree of change in the tack value is considerably larger than the change in the flow value, and the present invention utilizes the temperature change characteristics of ink based on this knowledge to perform multicolor wet overprinting. A method of performing multicolor wet overlapping printing by an offset printing method in which an ink image is transferred from the plate surface of a plate cylinder disposed on a printing plate to a blanket surface, and then transferred from the blanket surface to the surface of a printing medium, the method comprising:
Among the multiple inks that are overprinted on the surface of the printing material, the temperature of the last ink to be printed on the surface of the printing material, which is wet from the already printed ink, is determined first. The temperature of the ink to be printed is higher than that of the ink to be printed, and the temperature of the ink of the upper layer is higher than the temperature of the ink of the lower layer in the relationship between each ink when overprinted on the surface of the printing material. As a result, a printing method has been completed which is characterized in that a tack difference is provided between each ink, and multicolor wet overlapping printing is performed on the surface of a printing medium using the ink having the tack difference.

FIG. 1 is a graph showing the degree of change in tack value due to temperature change of white ink and yellow ink.
Figure 2 shows the flow value (1 in the spread meter) of the same white ink and yellow ink as the temperature changes.
2 is a graph showing the degree of change in the spread diameter of a certain amount of ink after a certain amount of minutes. In both cases, the W line represents the degree of change in white ink, and the Y line represents the degree of change in yellow ink.

According to these graphs, the tack value of both inks changes greatly with a slight temperature change, whereas
It can be seen that the flow value remains almost unchanged. Differences in tack values of inks (when overprinted on the surface of a printing material, the lowest layer of ink has the highest tack value, and the higher the layers from the bottom layer, the lower the tack value) Considering that if the difference in tack of each ink used is usually 1 to 3 or more, almost good multicolor wet overprinting is possible.
It can be seen that this method of varying the tack difference of each ink by varying the temperature of each ink does not substantially affect ink properties such as flow value and color density.

Next, examples of the present invention will be described.

Example 1 Primary color printing of orange youth cans was carried out continuously on a flat chromium-treated steel plate under the following conditions.

Printing board; 4-color process, 150-line screen, PS
Version (Liscoat-S, Liscoat-A
-1 manufactured by Fuji Yakuhin Co., Ltd.), the original image is a combination of a picture of mandarin oranges and a picture of mandarin oranges in a pot.Printing ink: Metal ink Cyan color Magenta color Yellow Navy blue Tatsu of each of these inks at 17℃ The values are cyan 30, magenta 28, and yellow, respectively.
27, dark blue 23. Under these conditions, the wet trapping rate (%) (described later) when printing with magenta ink and then yellow ink was 36%.

Using four offset presses, the chromed steel plate was fed into each press in succession, with the first press injecting cyan ink, the second press magenta ink, and the third press injecting magenta ink. Images and text were printed sequentially on a chromed steel plate using yellow ink on the fourth press and dark blue ink on the fourth press.

Here, the cyan ink and the magenta ink were used at room temperature (at 17°C), but the yellow ink and the navy ink were heated to 19°C by heating with hot air. The tack values of the yellow ink and the dark blue ink at 19°C were 23 and 20, respectively.

The resulting print was free from ink turbidity and halftone dot entanglement, and had extremely good reproducibility.
The wet trapping rate (%) when yellow ink was printed on magenta ink under these printing conditions (magenta ink at 17°C, yellow ink at 19°C) was 71%.

Example 2 The primary color printing of the orange nectar can was the same as in Example 1, except that the composition of the original picture of mandarin oranges and mandarin orange nectar in the container and white, navy blue, magenta and yellow inks were used as printing inks. Under these conditions, four-color wet overprint printing was performed on a chromium-treated steel plate. The tack value of each ink at 17℃ is 46 for white, 24 for dark blue, 22 for magenta,
Yellow ink was 20, and the magenta ink and yellow ink had tack values of 19 and 18, respectively, at 19°C.

The resulting print had no ink turbidity or halftone dot entanglement, and had extremely good reproducibility of the original image.

In the above example, the temperature of the ink used in the third and fourth printing was higher than the temperature of the ink used in the first and second printing. A temperature difference may be given between the two places or between the third and fourth places, or a temperature difference may be given at two places such as between the second and third places and between the third and fourth places. good. Furthermore, temperature differences may be provided between all inks. These are determined by considering the properties and printing suitability of the printing ink.

In addition, in the above example, the ink temperature is 17℃.
Although we chose 19°C, this was due to seasonal factors during the experiment period; it goes without saying that during periods of high temperature, such as summer, it is desirable to set the temperature to a higher temperature from an energy-saving perspective.

Furthermore, the means of heating the ink is not limited to hot air heating.
For example, any appropriate means may be used, such as passing a hot fluid through the inside of the ink roller or the inside of the plate cylinder.

Further, the means for creating a temperature difference between the inks is not limited to heating, and of course cooling one of the inks may be used. It is best to choose the one with better printing suitability in consideration of ink flowability, etc.

Furthermore, the wet trapping rate (%) mentioned earlier
The values calculated using the reflection density measurement method proposed by GATF were used.

The wet trapping rate P (%) according to the method proposed by GATF is determined by referring to Fig. 3.
Apply the first ink A onto the printing medium Z, and immediately,
First ink A' and second ink when second ink B' is applied so that a portion overlaps with first ink A'
Reflection density of the overlapping part of B′ (i.e. secondary color density)
is D, and the reflection densities of the first ink A' and the second ink B' (i.e., the first ink density, the second ink density) are A and B, respectively, and the following formula is used: P (%) = D - A/ Defined as B×100.

As described above, the present invention enables multicolor wet overlapping printing on the surface of an article without adversely affecting printability and print finish, greatly increasing the commercial value of the article to be printed, and furthermore, drying the printing ink. Since the baking process only needs to be done once, an energy saving effect can also be achieved.

The object of the present invention is not limited to metal cans, but also includes metal plates or articles, plastic sheets, films, containers, paper, laminates of two or more of the above-mentioned materials, or containers made from these materials.

[Brief explanation of the drawing]

Figure 1 is a graph showing the degree of change in tack value due to changes in ink temperature, Figure 2 is a graph showing changes in ink temperature and flow properties, and Figure 3 is a graph showing changes in ink temperature and flow properties.
FIG. 3 is an explanatory diagram of a method of calculating a wet trapping rate by reflection density measurement proposed by GATF.

Claims (1)

[Scope of Claims] 1. Multicolor wet overlapping printing using an offset printing method in which an ink image is transferred from the plate surface of a plate cylinder disposed around the blanket cylinder to the blanket surface, and then transferred from the blanket surface to the surface of the printing material. In this method, the temperature of the last ink to be printed on the surface of the printing material, which is wet from the already printed inks, is determined first, among the plurality of inks that are overprinted on the surface of the printing material. The temperature of the ink that is printed on the surface of the printing material is set higher than that of the ink that is printed on the surface of the printing material, and the temperature of the ink that becomes the upper layer in the relationship between each ink when overprinted on the surface of the printing material is set to be higher than that of the ink that is printed on the surface of the printing material. A printing method characterized by creating a tack difference between each ink by raising the temperature to a temperature higher than that of the ink, and using the inks with the tack difference to perform multicolor wet overlapping printing on the surface of a printing material.