At present, a new round of scientific and technological revolution is gaining momentum, information and network technologies are advancing by leaps and bounds, and various business models are in the ascendant. The economic foundation and objective environment on which my country's printing industry relies for survival and development are undergoing profound changes. At the same time, with the continuous integration of digitization, intelligence, greening and printing technology, as well as the gradual maturity and localization of inkjet digital equipment and pre-press intelligent software, domestic printing companies have ushered in a great opportunity to achieve digital transformation.
In order to accurately grasp the new market situation, share new technological achievements, and explore new directions for development, on June 13, 2019, "Digital Printing Creates a Smart linked Future—2019 Founder Electronics Digital Printing National Tour" hosted by Beijing Peking University Founder Electronics Co., Ltd. The first "Seminar" officially kicked off in Beijing.
In order to improve the design and quality of printed matter, printing plants often use spot color inks when printing trademarks, packaging, and promotional materials to ensure the color consistency of the printed matter and meet customer requirements. Next, let’s discuss printing specialties with you. The reason for the printing color difference of colored ink.
1. Printing process
01Ink layer thickness and ink balance
The control of ink hue during the printing process is mainly achieved by controlling the thickness of the ink layer. When the thickness of the ink layer changes by about 0.1μm, it will cause a color difference of △E=1.5~4.5NBS. Obviously, this impact is very large. The ink color reproduction of offset printing is closely related to the balance of ink and ink. Under the same ink volume, more water and less water will affect the depth of the color. It is crucial to correctly grasp the ink and ink balance and pay special attention to the PH value of the wetting solution. The principle of water consumption is to use the smallest possible water supply without getting dirty.
02Printing pressure
The amount of printing pressure has a great influence on the degree of ink transfer from the printing plate to the paper. When the printing pressure is insufficient, the ink transfer is insufficient and it is not suitable for printing; when the printing pressure is too high, due to the The ink spreads to the blank parts other than graphics and text, and the ink transfer rate not only cannot be improved, but also brings other disadvantages, and it is also not suitable for printing. only within the appropriate printing pressure range can we produce prints with thick ink layers, clear images, rich tones and good color reproduction.
03Printing speed
The increase in printing speed will shorten the contact time between the printing surfaces, make the dots virtual, reduce the ink transfer rate, and reduce the printing quality. In order to ensure full contact with the printing surface and improve printing quality, it is required to control the printing speed under a certain printing pressure to obtain a stable ink layer thickness.
04Dry density difference
For the same paper, the density of the newly printed proofs is higher, but the density value of the proofs after a period of time will decrease as the ink dries and the smoothness decreases. Due to the different density values of the ink layer before and after drying, the tones of the printed images are also different.
For newly printed products, the ink is still in a wet state, and there is a difference between the ink state and the dry state. This is because the newly printed ink layer has a certain leveling property, so the surface reflection is mainly specular reflection, which looks bright and glossy. When the ink layer is in a dry state, the surface reflection is mainly diffuse reflection, and the color is naturally duller than when it was just printed. Therefore, the ink color of printing proofs is generally slightly darker than that of standard proofs, but the exact depth must be controlled digitally. When proofing, measure the density value of each color just printed. When printing, refer to these density values for printing, so that the two colors can be printed. The ink color is close to the same. A density meter with a polarizing filter can eliminate the light generated by specular reflection on the surface of the ink layer. The measured wet color density is very close to the dry color density. The measured density value is very little affected by the dryness and wetness of the ink layer.
2. Surface finishing of printed matter
Surface finishing is to perform appropriate processing on the surface of printed matter to improve the light resistance, heat resistance, water resistance, wear resistance, folding resistance and chemical resistance of the printed matter; increase the gloss and artistic sense of the printed matter; and protect the printed matter. And the function of beautifying printed matter and increasing the value of printed matter.
The surface modification methods of packaging products mainly include glazing (printing varnish, coating varnish, matt varnish, UV varnish, water-based varnish, etc.), waxing, and coating (glossy film, matte film) , concave and convex embossing, hot stamping, etc. After the printed matter undergoes these surface treatments, there will be varying degrees of changes in hue and saturation, that is, differences in density. These changes can be divided into physical changes and chemical changes. The physical changes are mainly reflected in the increase in specular reflection and diffuse reflection capabilities on the product surface. Generally speaking, when covering with glossy film, applying bright varnish and UV varnish, the color density increases; when covering with matte film, applying matte oil, the color density decreases. Chemical changes mainly come from the organic solvents contained in the coating glue, water-based varnish, and UV varnish. They will combine with the ink particles on the printed matter to change the color of the ink layer.
3. Printing materials
01 Paper whiteness
Factors that affect paper whiteness include:
① Whiteness of slurry: the most important influencing factor.
②Dye: The dye should be selected so that it is near the main wavelength for measuring whiteness and does not affect its reflectivity, that is, it does not affect the whiteness of the paper.
③ Filling: depends on its type and grade.
④ Coating: The whiteness of coated printing paper is determined by the whiteness of the base paper, the whiteness of the coating, and the coating amount.
Papers with different whiteness and certain colors (such as some papers that are bluish or yellowish) have different effects on the color presentation of the printing ink layer. Therefore, in actual production, paper with the same whiteness should be used for printing to reduce the impact of paper whiteness on printing color.
02 Smoothness and gloss of paper
From the perspective of the impact on the quality of printed matter, there is a very direct relationship between the gloss of the paper and the gloss of the printed matter. Regardless of the type of ink, the gloss of the printed matter increases with the increase of the gloss of the paper itself. The glossiness of paper is directly related to the inking efficiency of the paper. Paper with high gloss can achieve higher printing density than paper with low gloss when using the same ink film thickness on the paper surface. Therefore, there is a close correlation between the gloss of the printed matter and the gloss of the paper itself.
03Ink acceptance and absorption properties of paper
Ink receptivity refers to the ability of the paper surface to receive transferred ink instantly when it is pressed on the printing press during the printing process. It is closely related to three aspects of paper performance: the ability of the paper surface to accept wetting from printing ink; the ability of the paper surface to absorb certain ink components; and the ability of the paper surface to fix and retain a uniform ink film. The ink absorption performance of paper occurs in a long period of time from the time when the ink comes into contact with the paper to the time when it is completely solidified on the paper surface. It is related to the absorption of low-viscosity components in the ink by the capillary pores of the paper and the transfer of certain components in the ink to the paper. related to internal osmosis.
Printing pressure, printing time, ink viscosity, and paper capillary radius will all affect the paper's ability to absorb ink. When the same ink is printed on paper with different absorbencies under the same conditions, there will be different printing densities. There is a pore structure formed by anisotropic multi-phase complex structural elements on the surface of paper. In order to obtain good uniformity and smoothness on the paper surface, paints of different thicknesses are generally coated on the paper surface. The nature and thickness of the coating determines the ability of the paper surface to absorb ink. Different absorption capacities lead to differences in the color of the printing ink layer.
4. Properties of ink
The final effect of the printed matter is closely related to the physical and chemical properties of the ink. The components of the ink determine the properties of the ink:
01The size of pigment particles and their degree of dispersion
Although the role of ink film capillaries is an important factor in forming the gloss of printed matter, the apparent size of the pigment particles in the dispersed state is more important, as it directly determines the state of the ink film capillaries.
Therefore, the pigment particles are small and well dispersed, which is beneficial to forming a smooth ink film and is also very beneficial to improving the gloss of the printed product.
02The viscosity of the connecting material and the pigment content
According to the principle of interface chemistry, the capillary penetration rate is inversely related to the viscosity of the liquid, that is, the penetration rate decreases as the viscosity increases. The capillary network structure formed between ink pigment particles is an important aspect that determines the gloss of printed matter. At the moment of imprinting, the ink is integrally pressed into the larger pores of the paper; after imprinting, the connecting material begins to separate from the ink and penetrates into the smaller pores of the paper. Therefore, the size of the ink film capillary determines the amount of separation of the connecting material. The role of the capillary in retaining the connecting material is much greater than the printing pressure in pressing the connecting material into the pores of the paper.
03Drying time
The rapid drying of the ink film on the paper surface can reduce the amount of connecting material penetrating into the pores of the paper, thereby improving the gloss and smoothness of the ink film. The high gloss of the ink film means that the degree of specular reflection on the surface is relatively high, so that the human eye can see much less white light reflected on the surface in most cases than the ink film with low gloss, making the color saturation more High, so prints with high gloss look more colorful and full. Most of the printing ink layers of spot color inks are translucent or opaque. When selecting the ink formula, the impact of the light transmittance of the ink layer on spot color printing must also be taken into consideration based on the actual situation.
The above are the reasons for the printing color difference of spot color inks shared with you. There are many factors that cause the printing color difference of spot color inks, but the main ones are: material performance, ink properties, printing conditions, and surface finishing of the printed matter. These factors will affect Color reproduction during spot color printing.