How to Control Overlapping Chromosome in Package Printing

In the packaging printing, the color effect of printed matter has a very important influence on the product packaging. It will not only enhance the quality of the product packaging, but also attract consumers and enhance the user's desire to purchase. However, in the packaging and printing, sometimes the printing factory and the customer both agree that the printing color is satisfactory. When printed on the packaging of the specific product, the color is deviated, sometimes the difference is still relatively large, so that the packaging of the product is not satisfactory, which is exactly where What's wrong? There are no exceptions in checking printing equipment, materials, and operating techniques. In fact, this is a phenomenon of metamerism in color science. From this it can be seen that metamerism has a great influence on packaging printing. Therefore, it is necessary to fully understand the principle and control method of this phenomenon and avoid this phenomenon of color aberration. Loss caused by packaging and printing manufacturers.

Chromatic different spectrum and its principle

Each object has its own fixed optical properties, that is, which color light it absorbs, and the nature of the reflected light is fixed. The color of each object is fixed in the full spectrum of sunlight. The so-called intrinsic color does not change, but refers to the optical properties of the object and the color appearing in sunlight. However, when the spectral composition of the light source is changed, both the monochromatic light of a certain wavelength range is missing in the light source, and the color light of this wavelength range is the color light reflected by the optical characteristics of an object. Under the light source does not show its inherent color, and presents different colors. This is when a pair of colors appear in the same color under a certain light source, but under another light source, the color it presents changes, this phenomenon is called metamerism. In this change, the spectral data of the object itself does not change, that is, the spectral data describes the surface properties of the colored object. Unlike the observer, the copying method differs from the observer in that the copying method has no effect, and the object color and reflection (transmission) ) The spectral power distribution of light is related but not one-to-one, and thus many light energy with different spectral distributions cause the same color sensation (ie, color mixing metamerism) of the human eye.

In color printing, the three primary colors YMC are usually used to simulate the reproduction of various colors in nature. However, for the human eye, the RGB color light is most sensible, that is, the color recognition method is based on the principle of additive color. Therefore, for the human eye, the color light and the color material are equivalent, which produces a phenomenon of metamerism, which is mainly due to the low resolving power of human eyes.

The influence of metamerism on packaging printing

The same-color spectrum phenomenon has a great influence on the packaging and printing of goods. For example, in the printing and packaging industry, many of the exquisitely printed packaging boxes are uniform in color and accurate, but in the hands of major shops or users, they find that the colors are quite different. These will make users doubt the authenticity of the goods, require returns and even complaints, the credibility of the natural business is also damaged, and in fact this phenomenon is caused by the phenomenon of metamerism in printing, not counterfeit goods, but consumers do not understand the The reason, therefore, should pay attention to this issue in packaging printing.

Chromophore color has a very important theoretical and practical significance in color reproduction technology. Because in actual production, the colorant used in the reproduction may not be the same as the color of the standard sample (original) color; even the same product in the same color, because of the different production time, the color material and formulation used, There are often big differences. The same color reproduced with different colorants may have different spectral reflection curves (transmission curves) (ρ1≠ρ2). For example, there are many kinds of color packaging printing manuscripts (oil paintings, ink paintings, and color photographs, etc.), but the colors used for copying the originals are yellow, magenta, cyan, and black, and the white color of the ink and the colors of the originals. The material is completely different. Therefore, there are a large number of metamerism phenomena. In color packaging printing, the neutral ink equivalent to the black ink is often obtained by overprinting with three primary colors of ink; or the same visual effect is obtained by directly replacing the three primary colors ink with a black ink; both have the same color, but do not have the same spectral reflection curve. So they are all metameric colors. It can be said that the color package printing is completely a method of copying the manuscript with metameric colors.

Chromophores are difficult to avoid in packaging and printing, and they can only be controlled. We know that the final color effect of prints in printing is determined by the inks and substrates (such as paper), so they are also the main factors that cause metamerism, so we must pay attention to these two aspects. In terms of ink, due to the development of modern packaging printing toward multi-color and anti-counterfeiting, in addition to the yellow, blue, black, and black base colors, there are more and more spot colors. Different batches of spot-color inks are prone to metamerism after printing, so special attention should be paid to this issue in spot color ink modulation, which is an important factor affecting quality. Also, ordinary four-color printing uses different batches of ink, and even though the conditions such as the printing color sequence are the same, metamerism occurs. Therefore, regardless of spot color or four-color printing, the same brand of ink should be used as much as possible when printing. When the same color spectrum is found, it is timely reflected to the supplier, and it is required to provide the same ink in order to minimize or control the same-color different spectrum. phenomenon.

However, in actual packaging and decoration printing, there will be a certain color difference from three primary colors inks with spot colors or three primary dot dot area ratios with spot colors. For packaging and decorating printing, the color difference should be allowed when the replica and the standard sample (original) are matched with the metamerism color. However, the color difference between the replica and the original should be controlled as far as possible, and it should be limited to the allowable range. Inside. In the paper (especially colored paper), the nature of the paper has a great influence on the color of the ink printing, that is, the same ink printed on different paper will produce different color effects. Among them, the main factors affecting the color difference of ink printing are the whiteness, brightness, and absorption of the paper. Differences in properties such as paper color also cause metamerism. Therefore, it is very important to achieve the same color and the same performance parameters as the standard when producing paper. However, due to the current quality control of color in papermaking companies, most of them use only the color difference value under one observation condition to evaluate the color isochromaticity, regardless of the metamerism problem. Therefore, in the printing, a product should use as much as possible the same batch of paper of the same manufacturer to reduce and control the heterochromatic phenomenon caused by the paper. When looking at the sample with the customer, the observation of the color draft and the sample must be performed under the same standard light source to avoid color deviation due to different light sources, which should be noted in the printing.

Application of metamerism

Chromophores have a detrimental effect on packaging printing and should be controlled during printing. However, in the printing of anti-counterfeit packaging, the same-color metastasis phenomenon also has its advantageous aspects. For example, from the perspective of color application technology, since the different spectral stimuli can produce the same viewing angle response, color matching can be obtained without using the same material. Therefore, by using metamerism, non-toxic pigments can be used in place of toxic pigments, and inexpensive pigments can be used instead of expensive pigments for color reproduction, thereby providing more favorable consumables for packaging printing. In addition, metachromatic spectrum ink is also a special anti-counterfeiting ink newly developed and developed. Using this ink printed graphic, different graphic sources can be produced under different light sources or changing the light direction. If it is under the sunlight, it is a kind of color. Under the irradiation of ultraviolet rays or other special lights, it becomes another color. It changes color with the change of the light source and the light, so that the printed matter has a good anti-counterfeiting function. Has been widely used in the printing of banknotes and coupons, such as the fourth set of renminbi issued in China has used the same-color different spectrum ink, if this ink is used in the packaging and printing of high-end goods, it will also enhance the product The anti-counterfeiting effect.

Author/Lin Qishui

Source: Guangdong Packaging