JP2007261239A - Offset ink printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing method which enables the reproduction of a color range wider than a color reproduction range of RGB expressed by conventional four-color printing of yellow, red, indigo and black processes. <P>SOLUTION: An offset ink printing method excellent in high-chroma color reproduction is characterized as below. In offset printing, either two or three of yellow ink, red ink and indigo ink, and black ink are used. A density value of yellow is in the range of 0.85-0.91; a density value of red is in the range of 0.88-0.94; and a density value of indigo is in the range of 0.84-0.90. When printing is done by singly using or superposing the respective color inks within the above ranges, chromaticity (JIS Z 8729) based on an L*a*b* colorimetric system, and chromaticity of overprinting using the two-color inks fall within specific ranges, respectively. Additionally, the yellow (a), the red (b) and the indigo (c) have specific reflection factors, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an offset ink printing method comprising four colors of yellow, red, indigo and black, and relates to a printing method using an ink system having four colors and excellent color reproducibility.

The IT revolution that began in the 1990s has led the environment surrounding the printing site to the direction of digitalization. By this digitization, workflow of conventional printing methods (photographing, positive, scanning, data, design, EPS)・ Imposition, film, printing plate, printing) was a multi-stage process, but it has succeeded in dramatically shortening the process with digital camera shooting, DTP, CTP, and printing. As a result, “RGB” conversion of the submitted data is being standardized, and the current situation is that the data to be handled is shifting to a wider color reproduction region.
However, in lithographic offset printing consisting of four process colors (CMYK) of yellow, red, indigo and black, which are currently mainstream, the color reproduction area is necessarily narrower than that of RGB because of the hue due to subtractive color mixing. The difference in color reproducibility between digital data and printed matter became a problem.
In particular, in paper printing (especially newspaper printing) using penetrating dry ink, there is a problem of whiteness and smoothness of paper, and the color reproduction area becomes narrower than that for coated paper. The difference in color reproducibility with the sample printed matter becomes a serious problem.

As means for solving this, in Patent Document 1, a printing method using an ink set of 5 to 7 colors is established as a high-saturation printing system. As a printing method using an ink set having each specified hue, process 4 colors are used. 6 colors (hexachrome printing) with orange and green added to 7 colors and 7 colors (high fidelity printing) with orange, green and purple added to 4 process colors have been established. In addition, as represented by hexachrome ink, as a means of expanding the color reproduction area, a technique such as adding a fluorescent pigment to a part of the color is used. However, deterioration of printability (transfer defect, gloss reduction, etc.) There are also disadvantages such as fading of printed matter due to insufficient light resistance. Furthermore, the number of ink colors used is 6 or 7, and an expensive multicolor printing machine with 6 or more printing cylinders is required. It is an indispensable condition, and it is limited to using this system due to huge capital investment and complicated color management to start a new one.

JP 2001-260516 A

The present invention has been made in order to solve such problems in the prior art, and the problem is that an RGB color reproduction region using a four-color printing machine that has been widely used in the past. Is to provide an offset ink consisting of four process colors of yellow, red, indigo and black, and an offset ink printing method using these.

In general, in order to expand the color reproduction region, it is necessary to approximate the ideal spectral reflectance curve of each color.
That is, the wavelength range in which a person recognizes color is 400 nm to 700 nm light (this wavelength is referred to as visible light). In yellow ink, the reflectance in the wavelength range of 500 nm to 700 nm is 100%, and the wavelength range of 400 nm to 500 nm. The red ink has a reflectance of 0%, and the red ink has a reflectance of 100% in the wavelength region of 400 nm to 500 nm and 600 nm to 700 nm, and a reflectance of 0% in the wavelength region of 500 nm to 600 nm. Therefore, it is said that it is ideal that the reflectance in the wavelength region of 400 nm to 600 nm is 100% and the reflectance in the wavelength region of 600 nm to 700 nm is 0% (the spectral reflectance of the ideal process ink) Curves are shown in Table 4).
However, the reflection spectrum of the ink composition for offset printing of yellow, red, indigo and black, which is currently used in four process colors, is far from the ideal reflection spectrum. Since there is unnecessary absorption in the part that must be completely reflected, a turbid component of the ink exists, and the color reproducibility is narrowed.
Therefore, in the present invention, any two or three of yellow ink, red ink and indigo ink, and offset printing using black ink, each density value of yellow, red and indigo is set to 0.85 for yellow. ~ 0.91, red is 0.88 ~ 0.94, indigo is 0.84 ~ 0.90, when each color ink is printed individually or by overlay, it depends on L * a * b * color system Chromaticity (JIS Z 8729)
Yellow ink, L *: 77 to 85, a *: -1 to -9, b *: 60 to 70
Red ink, L *: 54-60, a *: 46-52, b *: -5-11
Indigo ink, L *: 55-61, a *: -23 to -28, b *: -26 to -32
And the chromaticity of the two ink overprints of the above ink is
Red * yellow ink, L *: 52-60, a *: 37-43, b *: 27-34
L *: 52 to 57, a *: -36 to -42, b *: 20 to 26
L *: 38-45, a *: 11-18, b *: -30 to -36
An offset ink printing method excellent in color reproduction with high saturation, characterized by being in the range of the above, comprising the combination of the three colors, the combination of the two colors and the black ink, and the three colors The present invention relates to an offset ink printing method capable of expanding the color space of the L * a * b * color system by printing in combination with black ink.
Further, the present invention relates to an offset printing method in which (a) yellow, (b) red, and (c) indigo have the following reflectance.
(A) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the wavelength region of 400 nm to 480 nm is 1 to 20%, and the reflectance in the wavelength region of 530 nm to 700 nm is 90 to 100%. A yellow ink containing 5 to 15% of a yellow phase compound having a reflection spectrum.
(B) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the maximum reflectance in the wavelength region of 400 nm to 500 nm is 50% to 100%, and the reflectance in the wavelength region of 500 nm to 560 nm. A red ink containing 15 to 20% of a red hue compound characterized by having a reflection spectrum of 1 to 20% and a reflectance of 630 nm to 700 nm of 90% to 100%.
(C) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the reflectance in the wavelength region of 400 nm to 530 nm is 50 to 100%, and the reflectance of 600 nm to 700 nm is 1 to 30%. An indigo ink containing 5 to 15% of an indigo hue compound characterized by having a spectrum.

  By using the offset ink printing method provided by the present invention, it is possible to reproduce a wider color region than the RGB color reproduction region expressed by the conventional four-color printing of yellow, red, indigo and black ink processes. Become. Further, in the present invention, since a fluorescent pigment is not used as a means for improving the color reproduction region of the printed material, a highly saturated printed material can be obtained without deteriorating printability, fading with time of the printed material, and the like.

Next, the present invention will be described more specifically with reference to preferred embodiments.
The present invention comprises a pigment, a vehicle component obtained by heating and dissolving a synthetic resin, a vegetable oil, and a petroleum solvent together with a gelling agent such as aluminum stearate or aluminum chelate as necessary, and an auxiliary agent such as a friction-resistant agent. It is an offset ink consisting of four colors of yellow, red, indigo and black, and is an ISO standard newspaper color paper for newspapers such as Nippon Paper Industries' newspaper paper (based on JCN paper, weighing 43 g / m ² , L * : 82, a *: -0.4, b *: 4.6), yellow, red, and indigo colors Gretag Macbeth Spectro Eye (45/0, D50, 2 degree field of view: Status T) densitometer When the density values measured in the above are in the range of 0.85 to 0.91 for yellow, 0.88 to 0.94 for red, and 0.84 to 0.90 for indigo, and each single color Chromaticity (JIS Z 8729) according to the L * a * b * color system of the overprinting of L *: 77 to 85, preferably yellow ink 78-83, a *: -1 to -9, preferably -2 to -8, b *: 60 to 70, preferably 62 to 68, red ink, L *: 54 to 60, preferably 55 to 58, a *: 46-52, preferably 47-50, b *: -5 to -11, preferably -7 to -10, indigo ink, L *: 55 to 61, preferably 56 to 60, a *: −23 to −28, preferably −24 to −27, b *: −26 to −32, preferably −27 to −30, and further, red ink × yellow ink, L *: 52 -60, a *: 37-43, b *: 27-34, indigo ink x yellow ink, L *: 52-57, a *: -36 to -42, b *: 20-26, It is characterized in that it is in the range of L *: 38 to 45, a *: 11 to 18, b *: −30 to −36 by printing with indigo ink × red ink.

As a method for expressing the color reproduction area, an XYZ color system (CIE 1931 color system), an X ₁₀ Y ₁₀ Z ₁₀ color system (CIE 1964 color system), an L * a * b * color system (CIE 1976), Hunter Lab color system, Munsell color system, L * u * v * color system (CIE1976), and the like.

Ｃに関しても同様に、絶対値が大きくなるに従って色鮮やかになり、値が小さくなるにつれてくすんだ色になることを示している。 In the L * a * b * color system, “brightness” is expressed by L * as the degree of brightness that can be compared regardless of hue, and indicates that the color becomes brighter as L * increases and becomes darker as it decreases. . In addition, “hue” which differs depending on each color is indicated by a * and b * values, a * indicates red (+) to green (−) direction, and b * indicates yellow (+) to blue (−) direction, In each direction, the color becomes brighter as the absolute value increases, and the color becomes dull as it approaches 0. This makes it possible to digitize one color using L *, a *, and b *. In addition to “lightness” and “hue”, there is “saturation (C)” as a method for digitizing the degree of vividness, which can be obtained by the following calculation formula.

Similarly, C shows that the color becomes brighter as the absolute value increases, and the color becomes dull as the value decreases.

All color reproduction areas that can be represented by a single printed matter (including color spaces other than printed matter) are called color rendering regions (gamut). The simplest way to represent gamut is as follows: a * is the horizontal axis, b * vertical axis In the two-dimensional space, the solid color part (yellow, red, indigo) and the solid color overprinting part (yellow x red, red x indigo, indigo x yellow) total of 6 colors a * vs b *, It can be expressed by the plotted hexagonal area. The larger the gamut area, the wider the color reproduction area.

In the present invention, the color space (color space) in the L * a * b * color system is represented by the horizontal axis a * as a color rendering region considering not only the two dimensions of a * and b * but also the lightness “L *”. Is expressed in 10 step increments in the range of -80 to +80, vertical axis b * in the range of -80 to +80, and height L * is represented by slicing in increments of 10 steps from 0 to 100. The color reproduction area indicating the number is schematically expressed, and the larger the number of reproduced colors, the wider the color rendering area that can be reproduced by ink.

  Japan Color is a standard color for printing established by the ISO / TC130 National Committee. In Japan Color for Newspapers (hereinafter referred to as JCN), ISO 12642 SCID chart (928 colors), a pattern according to ISO 12647 ( 80 color) and color measurement values (L * a * b * values) using “JCN2002 chart” designed to examine the reproduction of important printing colors (skin color, gray, vivid color) in newspaper printing Is shown. The printing conditions are based on the standard conditions of international standards ISO 2864-2 and ISO 12647-3 concerning newspaper printing. News inks and printing papers commonly used in Japan (the color characteristics of standard papers are determined in JCN) ) Is used. The L * a * b * values of yellow, red, indigo and single-color solid parts when printing JCN-compliant ink on JCN standard paper, and the C value calculated from them are yellow ink, L * : 77, a *: -4, b *: 58, C: 58, red ink, L *: 53, a *: 44, b *: 0, C: 44, indigo ink, L *: 58, It is said that a *: −23, b *: −26, and C: 35. At this time, the density of the solid portion is 0.86 for yellow ink, 0.89 for red ink, and 0.85 for indigo ink.

The yellow pigment used in the present invention is a disazo yellow compound such as CI Pigment Yellow 12, CI Pigment Yellow 13, and the like on a black ink printed within a density value range of 1.10 to 1.20. In addition, if the L * value has a transparency not exceeding 31 when the density of the yellow ink is overprinted in the range of 0.85 to 0.91, the secondary color and the tertiary color are overprinted. It is possible to obtain a good color reproduction region with little influence on the underprint ink.
Furthermore, it is also possible to use CI pigment yellow 83 as a complementary color by adding 0.5 to 10%, preferably 2 to 5% of the above yellow pigment.

  Examples of red pigments include, but are not limited to, rhodamine-based dyes such as rhodamine B, rhodamine 3G, rhodamine 6G, molybdenum, tungsten metal lake compounds such as C.I. Pigment Red 81 and C.I. Pigment Violet 1.

Examples of the indigo pigment include phthalocyanine compounds such as CI pigment blue 15: 3 and CI pigment blue 15: 4. Further, CI Pigment Green 7 may be used as a complementary color by adding 5 to 15%, preferably 8 to 11% of the indigo pigment.
The copper phthalocyanine compound, which is a cyan pigment used in the present invention, is a substance exhibiting a crystal polymorphism (homogeneous heterocrystal), and α, β, γ, ε, π, τ, ρ, χ depending on the crystal structure. However, it is preferable to use a β-type having excellent crystal stability and dispersibility, and further a fine β-type copper phthalocyanine having a specific surface area of 74 m ² / g or more. preferable.

Examples of black pigments include carbon black, such as CI pigment black 7.
As the synthetic resin used in the present invention, rosin-modified phenol resin, petroleum resin, alkyd resin, rosin-modified alkyd resin, petroleum resin-modified alkyd resin, rosin ester and the like can be considered. Preferably, a rosin modified phenolic resin is used. The rosin-modified phenol resin is not particularly limited, but it is preferable to use a resin having a weight average molecular weight of 10,000 to 300,000. When the molecular weight is 10,000 or less, the viscoelasticity of the ink is lowered, and when it is 400,000 or more, the fluidity as the ink becomes insufficient.

Examples of vegetable oils include those derived from vegetable oils such as palm kernel oil, palm oil, cottonseed oil, peanut oil, palm oil, corn oil, olive oil, linseed oil, corn oil, soybean oil, safflower oil, and tung oil, Those thermal polymerized oils and oxygen-blown polymerized oils can also be used. Moreover, in this invention, these vegetable oils may be used independently and can also be used in combination of 2 or more type.

  The petroleum solvent used in the ink has an aromatic hydrocarbon content of 1% or less, an aniline point of 75 to 95 ° C, preferably 80 to 95 ° C, and a boiling point of 260 to 350 ° C, preferably 280 to 350. It is a petroleum solvent in the range of ° C. If the aniline point is less than 75%, the ability to dissolve the resin is too high, which is not preferable because the ink setting property is slow, and if it exceeds 95 ° C., the resin solubility is poor, so Meat etc. are bad and not preferable. When the boiling point is less than 260 ° C., the evaporation of the ink solvent on the printing press increases, and the transferability of the ink to a roller, a blanket, a plate, or the like deteriorates due to the deterioration of the fluidity of the ink.

  Furthermore, the offset ink composition of the present invention includes a gelling agent, a pigment dispersant, a metal dryer, a drying inhibitor, an antioxidant, an antifriction agent, an anti-set-off agent, and a nonionic surface active as required. Additives such as agents and polyhydric alcohols can be used as appropriate.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, the scope of the present invention is not limited to these description Example. In addition, the part of the following description represents a weight part and% represents weight%.

(Production of rosin-modified phenolic resin gel varnish A for offset)
38.5 parts of rosin modified phenolic resin (Arakawa Chemical Industries, Ltd .: weight average molecular weight 150,000, acid value 20, softening point 160 ° C.) in a four-necked flask equipped with a condenser, thermometer and stirrer, soybean oil 30 parts, 30 parts of AF Solvent No. 5 (manufactured by Nippon Oil Co., Ltd.) were charged, heated to 180 ° C., stirred at the same temperature for 30 minutes, allowed to cool, and ethyl acetoacetate aluminum as a gelling agent 1.0 part of diisopropoxide (ALCH manufactured by Kawaken Fine Chemical Co., Ltd.) was added and stirred at 180 ° C. for 30 minutes to obtain a rosin-modified phenol resin gel varnish A for offset (hereinafter referred to as gel varnish A).

Ink example (yellow ink)
In the formulation shown in Table 1, C.I. I. Pigment Yellow 12 (LIONOL YELLOW 1245-P, manufactured by Toyo Ink Manufacturing Co., Ltd.) was subjected to primary dehydration by gradually adding and kneading gel varnish A in a kneader at a temperature of 75 ° C. Next, vacuum dehydration was performed for 1 hour under conditions of a kneader temperature of 100 ° C. to 120 ° C. and a degree of vacuum of 76 mmHg, and secondary dehydration was performed so that the water content in the base ink was 0.5% or less. After dehydration, the remaining gel varnish A, AF solvent No. 5 and soybean oil were added, kneaded and diluted, and the undispersed base ink was taken out from the kneader. The extracted base ink was kneaded using a three roll with a roll temperature of 60 ° C. with a dispersed particle measuring machine (grind meter) to 7.5 μm or less to obtain yellow base ink 1. Next, gel ink varnish A, soybean oil, compound and AF solvent No. 5 were added to the base ink 1 according to the formulation shown in Table 2 to obtain yellow ink 1.

Ink Example (Red ink)
As with the yellow ink, C.I. I. A red base ink 2 was obtained using Pigment Red 81 (Funal Rose RNN-P manufactured by Fuji Kasei Co., Ltd.). Subsequently, to the base ink 2, gel varnish A, soybean oil, compound and AF solvent No. 5 were added according to the formulation shown in Table 2 to obtain red ink 2.

Ink Example (Indigo Ink)
In the formulation of Table 2, C.I. I. Pigment Blue 15: 3 (LIONOL BLUE FG 7330 manufactured by Toyo Ink Mfg. Co., Ltd.) was mixed with varnish, and after milling with a dispersed particle measuring machine (grind meter) to 7.5 microns or less, soybean oil, Compound and AF solvent No. 5 were added to obtain indigo ink 3.
A comparative newspaper ink was used as a comparative ink.

The transparency of the yellow ink was evaluated by the following test method.
On the black ink printed within the density value range of 1.10 to 1.20, the yellow ink density was printed in the range of 0.80 to 1.10, and the L * value was measured. The results are shown in Table 5.
The yellow ink of the example does not exceed L * even when the density value is increased to 1.10, and does not affect the black ink of the underprint, and can be said to have excellent transparency (L * has a value) The smaller the color, the more black it is, and the bigger the color, the whiter it is) On the other hand, L * is high in the comparative example, and it can be seen that the black ink of the underprinted ink is hindered because the yellow ink of the overprinted is opaque.

Printing Evaluation Test For the inks of the above examples and comparative examples, the solid density values of yellow, red, and indigo were yellow: 0.85 to 0.91, and red: 0.88 to 0.94 under the following printing conditions. , Indigo: Printing was performed within the range of 0.84 to 0.90, and the printed matter was evaluated. The ink used was a general offset newspaper printing ink, and was printed within a density range of 1.12 to 1.20.

結果を表３に示す。比較例と比べて実施例のＣ値が大きく、印刷物の彩度が高い。また、ａ*を横軸、ｂ*縦軸とした2次元空間に、各ａ*、ｂ*値をプロットし、２次元のガモットで比較した結果、実施例の色再現領域が広いことがわかる（図４）。
また、得られた分光反射率曲線を表６に示す。比較例の従来インキに比べ、実施例のインキの方が理想の分光反射率曲線に近くなっており、完全反射しなければならない部分の不必要吸収が少なくなっている。そのため、インキの濁り成分が減少し、色再現領域が広がっている（表７）。 Printing conditions Printing machine: LITHOPIA BT2-800 NEO (Mitsubishi Heavy Industries, Ltd.)
: Printing order: Ink->Indigo->Red-> Yellow Paper: Newspaper for newspaper: Ultralight paper (weighing 43 g / m ² ) (Nippon Paper Industries Co., Ltd.)
(Colorimetric value: L *: 82, a *: -0.4, b *: 4.6)
Dampening water: NEWSKING ALKY (Toyo Ink Mfg. Co., Ltd.) 0.5% tap water printing speed: 100,000 parts / hour

Measurement conditions for printed matter Concentration: Measure the density value of the solid (yellow, red, indigo, black) solid portion of the printed matter with Gretag Macbeth Spectro Eye (45/0, D50, 2 degree field of view: Status T).
Colorimetry: Gretag Macbeth Spectro Eye (45/0, D50, 2-degree field of view: Status T), single-color solid part (yellow, red, indigo) of printed matter and single-color solid overprinted part (yellow x red, red x L *, a *, b * values of indigo, indigo × yellow) are measured.
The C value was determined from the following formula using a * and b *.

The results are shown in Table 3. Compared to the comparative example, the C value of the example is large, and the chroma of the printed matter is high. In addition, as a result of plotting each a * and b * value in a two-dimensional space with a * as the horizontal axis and b * vertical axis and comparing them with a two-dimensional gamut, it can be seen that the color reproduction region of the embodiment is wide. (FIG. 4).
Further, Table 6 shows the obtained spectral reflectance curve. Compared to the conventional ink of the comparative example, the ink of the example is closer to the ideal spectral reflectance curve, and unnecessary absorption of the portion that must be completely reflected is reduced. Therefore, the turbidity component of the ink is reduced and the color reproduction area is widened (Table 7).

Claims (2)

In offset printing using any two or three of yellow ink, red ink and indigo ink, and black ink, each density value of yellow, red and indigo is set to 0.85 to 0.91 for yellow. Chromaticity according to the L * a * b * color system (JIS Z) when each color ink is printed individually or by superposition within the range of 0.88 to 0.94 for red and 0.84 to 0.90 for indigo. 8729)
Yellow ink, L *: 77 to 85, a *: -1 to -9, b *: 60 to 70
Red ink, L *: 54-60, a *: 46-52, b *: -5-11
Indigo ink, L *: 55-61, a *: -23 to -28, b *: -26 to -32
And the chromaticity of the two ink overprints of the above ink is
Red * yellow ink, L *: 52-60, a *: 37-43, b *: 27-34
L *: 52 to 57, a *: -36 to -42, b *: 20 to 26
L *: 38-45, a *: 11-18, b *: -30 to -36
An offset ink printing method excellent in color reproduction with high saturation, characterized by being in the range of the above, comprising the combination of the three colors, the combination of the two colors and the black ink, and the three colors An offset ink printing method that can expand the color space of the L * a * b * color system by printing in combination with black ink.
In offset printing using any two or three of yellow ink, red ink and indigo ink, and black ink, the reflectance of (a) yellow, (b) red, (c) indigo is The offset printing method according to claim 1, wherein the offset printing method is provided.
(A) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the wavelength region of 400 nm to 480 nm is 1 to 20%, and the reflectance in the wavelength region of 530 nm to 700 nm is 90 to 100%. A yellow ink containing 5 to 15% of a yellow phase compound having a reflection spectrum.
(B) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the maximum reflectance in the wavelength region of 400 nm to 500 nm is 50% to 100%, and the reflectance in the wavelength region of 500 nm to 560 nm. A red ink containing 15 to 20% of a red hue compound characterized by having a reflection spectrum of 1 to 20% and a reflectance of 630 nm to 700 nm of 90% to 100%.
(C) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the reflectance in the wavelength region of 400 nm to 530 nm is 50 to 100%, and the reflectance of 600 nm to 700 nm is 1 to 30%. An indigo ink containing 5 to 15% of an indigo hue compound characterized by having a spectrum.