Wear gold and silver for prints - the mystery of metal ink
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I remember 20 years ago, the 20th anniversary of Hong Kong’s freshman design school, so I wanted to have more eye-catching elements in the publicity materials. Since I have been working together for several years, as always, Mr. Lu is a designer. After you have come up with ideas, let me talk about the techniques that can be used and matched to achieve the best results. Since the designer used the stationery to make a robot as the theme, the author suggested that it is better to add a large area of metal feeling, and get a hot silver effect over the A3 area as the cover of the graduation annual magazine, and also have a screened hot silver. At that time, there were only two or three hot stamping machines in Hong Kong that could burn such large areas, and they all said that they had not tried to make such a large area of iron.
Finally, because I had to rush to the graduation exhibition, I had to make a hundred copies, and the rest had to solve it with Yinyin, which is the version I saw in the workshop. President Lu, the designer and I certainly collected this hot silver. The limited edition, I believe that there are not many people who have seen this hot silver version so far, and the metal ink used in printing silver has a big gap with the present, and the effect is more distinct from the shiny effect of hot silver. If there are so many different metal inks available today, you don't need to give up the original design, but there is no money and time for a good design. It is often impossible to achieve, and experience tells me that time is more than money. important.
The metal inks used today have been able to replace the more expensive materials such as aluminum foil or gold-plated materials. On the other hand, metal pigments are widely used, and metal effects can be achieved by different processes, such as replacing hot silver. Over the past decade or so, metal ink technology has also greatly improved the convenience and flexibility of printing, and has an advantage in cost. Since the content of metallic pigments in metallic inks is generally 2 to 4 times greater than that of ordinary inks, metallic inks are much more expensive than ordinary inks. Despite this, ink printing is still popular in the packaging and printing industry, because metal ink printing has the advantages of fast production speed and low cost compared with processes such as hot stamping and aluminized film printing. Therefore, many consumer product packaging, such as food, beverages, cosmetics, etc., use a lot of metal ink to stimulate the eye. It is also convenient to use, because there is no need to add or modify equipment, it can be produced like ordinary ink, improve efficiency, and save costs. Of course, the printing process I refer to is not just the lithography that Hong Kong people are familiar with, but also different technologies such as silk screen printing, flexo printing and gravure printing.
So what is the progress of metal ink today? Let me start with the structure of the metal ink.
Metal ink structure
A metallic printing ink is an ink prepared by replacing a pigment or a dye in a conventional ink with a fine metal foil, and has a metallic glittering effect. Typical metal inks are mainly gold and silver inks. Gold inks are generally added with copper pigments and zinc pigments. By controlling and changing their proportions, they produce inks such as green gold, crimson gold, and red gold; while silver inks are prepared by adding aluminum pigments.
The optical properties of metallic pigments are different from those of ordinary pigments, so the optical properties of the produced metallic inks are also quite different from those of ordinary inks. The color of ordinary ink does not change with the viewing angle, but the hue and brightness of metallic ink will change depending on the viewing angle. Therefore, when using the instrument to measure the color of the metallic ink, the general spectrodensitometer cannot be used. Instead, special spectrodensitometers for measuring reflective metals are used. If it is not clear, misunderstandings of color infrequencies will often occur.
To match the printing method
The effect of the metallic ink shining is the result of the combination of specular reflection and diffuse reflection of the metallic pigment. In order to achieve a better metal effect, the specular reflection of the metallic pigment should be increased to reduce the diffuse reflection. The effect of the ink reflection is mainly the size of the metal pigment particle size. The larger the size of the single pigment particle, the better the specular reflection effect, and the higher the gloss of the metal ink, but its hiding power and dot reproducibility will be lower. On the contrary, the smaller the size of the metal pigment particle size, the higher the hiding power and dot reproducibility of the metal ink, but the excessive gloss scattering of the edge causes the gloss of the metal ink to decrease. Therefore, the user needs to select a suitable particle size according to his own requirements, and the selection must be accompanied by a specific printing method. Different printing methods will definitely affect the shining effect of the metal ink, for example, the particle size is too large, during the printing process. If the ink is not transferred smoothly, it will cause the mesh to be clogged or the ink squeegee accumulates during the silk screen printing. The ink will also become thicker, which will affect the print color and the uniformity of printing. On the other hand, if the particle size is too small, it will easily cause the light to diffuse, causing the ink to lose the metallic luster and causing the printing effect to be not bright.
Experiments have shown that in silk screen printing, the size of the mesh should be about 3 times the average size of the metal particles. The metal foil particles in the metal ink can smoothly pass through the mesh under the action of the doctor blade. Generally, the average size of the metal ink particles is 15-20 μm, and the mesh size of the mesh is about 400/inch (the mesh size is about 60 μm). ), but with 400/inch mesh, the precision is not bad. There are obvious dog teeth on the side of the picture, but if you want the picture to be clear, you have to sacrifice the brighter effect of the large particles, and switch to the fine-grained metal ink in exchange for the smooth printing.
Distribution of metallic pigment particles
In addition, the particle distribution of the metallic pigment is also a factor affecting the optical properties of the metallic ink. When using metal inks from different manufacturers, although the particle size shown on the technical data is the same, the hiding power and metallic gloss of the metal ink after printing sometimes vary greatly, because different ink manufacturers are manufacturing metal inks. The particle distribution of the metallic pigment is sparse and dense. The same average particle size, the denser the particle distribution, the more neatly arranged the pigment, the better the gloss and hiding power of the produced metal ink, so the distribution of the particle by different metal pigment manufacturers will be the metal ink. The effect has a big impact. The uniform distribution of the metal sheets depends on the properties of the resin and solvent in the ink. Good resin can make the metal sheet distribute very evenly, but the ink made of poor resin has a very uneven distribution of metal particles. Under the microscope, the metal sheet can be seen sticking together, and the individual particles are very different. Difficulties, the metallic luster effect of the printed matter is greatly reduced.
Metal ink innovation
The shape of the metallic pigment particles in the conventional metallic ink is irregular, but since the shape of the metallic pigment particles is irregular and the edges are not smooth, the specular reflection effect of the particles is poor, and the diffuse reflection of the edges is severe, so the metallic luster and the covering of the metallic ink The corresponding force is also poor. The new type of metallic pigment is an approximately circular structure with uniform size and good specular reflection, while the metal effect and hiding power are excellent.
In some new metal inks, the metal foil particles are mostly long-shaped particles. Under the premise of satisfying the size, the particles of the shape can reduce the thrust required when the particles move in the ink medium, thereby achieving Reduce the viscosity of the ink. Because the metal ink does not become viscous due to an increase in the fineness of the particles. This is mainly because when the metal sheet is rotated or swayed during the flow, the energy required is higher than that of the ordinary particles. The larger particles need to have a large thrust when moving in the ink medium, so the viscosity of the ink is increased. If the ink is too thick, not only will the ink be affected when passing through the mesh of the screen, but also uneven printing density and sheeting during printing, whether on gravure or flexographic printing plates. Conversely, when small particles require only a small thrust, the flow can be smooth and natural, and the viscosity becomes very low. Larger metal particles can better enhance the metallic effect of the ink, but in order to achieve low viscosity and print uniformity, smaller particles are often required. Therefore, the choice between the two is often determined by the actual situation.
Recently, there is also an ultra-thin, non-floating electroplated aluminum paste, which is a very unique metal pigment, VMP (Vacuum Electroplated Metallic Pigment), which is produced by a special vacuum plating process to obtain a very smooth and extremely thin scale structure. Therefore, it has completely different metal effects from the copper and aluminum metal pigments produced by the conventional method. If used, a chrome-plated surface coating can be obtained, which is very metallic. At present, the use of VMP special bright aluminum paste, using VMP-containing ink as a substitute for aluminum foil paperboard during packaging printing, can save material costs.
Myths when using metallic inks
Then why do we sometimes use good metal ink, but the effect of printing is still not ideal, not enough to shine? In addition to the quality of the metal ink used, reasonable production practices are also important.
Designers often choose metallic colors other than gold and silver. The printers will use metal inks and four-color or other spot color inks to adjust the inks of the metal spot colors, but the metal materials used to produce metal inks are soft and thin metal sheets, and many printing operators. It is customary to stir the ink with some hard metal tools, and the metal material is sensitive to shearing force. Excessive shear force will cause the metal pigment particles to deform or form many fine particles, in order to avoid shearing force on the metallic pigment. The effect of the particles, when adjusting the metal spot color ink, use some relatively smooth tools, and avoid high-speed stirring, otherwise the transferred ink will lose its luster.
In addition, the ink medium (such as resin and solvent) used by the general ink factory in the production of metal spot color inks is mostly different from the metal inks that have been made, plus the metal color in the stirring as mentioned above. The ink is also different from the ordinary ink, so if you want to deal with a large number of packaging printing, you can get better results by directly ordering the metal spot ink to the ink factory.
Experience with metal inks
Since the materials used to make metal inks are all active metal materials, the chemical properties of metal inks are also very unstable, and they must be tightly sealed during use and storage to avoid absorbing too much moisture and being directly exposed to light for a long time. In lithographic printing, the use of an inappropriate fountain solution can also affect its sparkling effect.
In addition, the density of the metallic pigment is large, so the metallic ink is very easy to precipitate compared with the ordinary ink, and if it is not sufficiently stirred before use, it is not checked whether there is any sediment at the bottom of the ink tank before printing on the machine, and the printed matter is printed. Hue and gloss vary widely. Metal ink will be volatilized during the printing process, and the viscosity will gradually increase. In order to ensure the stability and good fluidity and transferability of the metal ink, it is necessary to regularly measure the viscosity of the ink and appropriately add solvent to keep the viscosity of the ink at Stable state.
The price of metal ink is much higher than that of ordinary ink, but the residual metal ink used in the ink residue will be found to have a significant decrease in gloss. Therefore, in the process of satisfying smooth production, it should be as many times as possible in the printing process. Add a small amount of metal ink to the principle of not breaking the waste.
In recent years, metallic color has been used in publicity materials and packaging products. In addition, printing machines in Hong Kong and the Mainland have set up five-color and six-color printing machines in the past ten years. It is more convenient for printing metallic colors, so there is no need to worry about time. The problem, in recent years, there are many new materials and technologies in this area. Let's talk about it later!