Printing ink viscosity and printing adaptability

In our daily packaging and printing production, because most of them only focus on the determination of viscosity, we neglect to check the stickiness (instead of just referring to the length of the filament pulled out during the bonding process, but the force at the time of bonding). It is not that the adhesion fastness of the printing ink is not good or the plate is dirty, or that the color density is worse than the printing, and the printing speed cannot be increased, and the former color printing ink film is pulled off, resulting in the printing ink film peeling off and staining. After the color, the authenticity rate decreases.

Because almost 80% of packaging printing ink in our country is a plastic fluid, it has very complex and difficult to define the viscosity, viscosity, and even the impact of the pH value and concentration and consistency will lead to the so-called viscosity. Along with the structure of various packaging printers and the different properties of various substrates, there are also various requirements for inks. Therefore, the relationship between the viscosity and viscosity of various types of printing inks and the suitability of packaging and printing is also interrelated and very complicated. In this regard, the author has followed his own years of practice, especially in nearly 85% of the time each year, visited hundreds of packaging and printing companies and printing ink companies in recent 10 trips, and companies that have met with hundreds of millions of years have also had annual output of less than 10,000 yuan. Yuan's home workshop. Although the way, method, speed, quality, and quantity of packaging printing vary, the knowledge, understanding, processing, and countermeasures involved in the viscosity and viscosity of printing inks vary.

On the other hand, in wet coastal areas and dry northern regions, in the winter and summer, especially in the rainy days and high-temperature weather, we have different requirements in terms of production technology, so that the ergonomics, including the obtained authenticity rate and output, will not change. In the same way, the prices sold are even more varied. Self-regulation in that industry is even more difficult to implement.

In addition to frequent testing, comparison, recording, and testing, the authors have visited the original Shanghai, which has been engaged in printing ink production for more than 50 years, in terms of viscosity and viscosity. Chief Engineer of ink factory, Mr. Yang Haijun, together with well-known domestic companies such as Fu Kang of Zhejiang, Dibang, Jinya of Jiangsu, Hengchang, Shenda, Dajiang of Shanghai, Yongfei of Shandong, Taixing of Fujian, Shenyang Printing Plant of Liaoning, Henan Bo Tao and other manufacturers of engineering and technical personnel, and even the first-line operating personnel conducted nearly a thousand face-to-face exchanges, from which to obtain a large number of very useful knowledge and practical new models of simple operation methods, subject to the recognition of experts and scholars in the industry. For this reason, only a rough introduction can be made here about the relationship between the printing viscosity and viscosity of the packaging and the suitability of the packaging printing, for the reference of colleagues in the packaging printing industry and the printing ink industry.

Printing ink viscosity and printing adaptability

The general theory of viscosity

Viscosity, whether it is for letterpress or flexographic inks, generally has a general rule except that it is obviously and strictly related to printing. High-viscosity inks, slow printing speeds, can only be applied to offset printing or letterpress, and manual Silk screen printing; low viscosity ink, fast printing speed, adapt to high speed rotary printing flex, gravure and offset printing.

Specific to the viscosity of flexographic inks and letterpress inks, it is not as clear as the distinction between flexographic inks and gravure inks. Usually the printer is slow and uses high-viscosity printing inks; printers have fast printing speeds and use low-viscosity printing inks. When the viscosity of the printing ink increases with the printing speed, the ink temperature increases and decreases after the ink roller rubs against the printing plate. When the ambient temperature rises, the viscosity of the ink gradually decreases. This uses the ink. When the temperature rises, the viscosity-decreasing behavior is referred to as the increase in the viscosity index. That is, the viscosity index is an indicator that the viscosity changes with temperature. For example, if the solvent oil forms a slurry at a low temperature, the methacrylic acid is added. The copolymers of esters and polar monomers rule out the occurrence of such failures. It works better if mixed with low molecular weight ashless dispersants. This prevents and eliminates the increase in the viscosity index and is often referred to as the viscosity index increasing agent. Therefore, a slightly higher viscosity does not affect the normal print job speed. Excessive viscosity not only affects the fastness of printing, but also affects the speed of printing.

In addition, the viscosity requirements of inks for packaging and printing substrates vary. Polyolefin substrates with low surface tension and high surface tension polyolefin substrates require surface treatment in the case of printing inks. In general, the former should select inks with low viscosity, and the latter should be reversed. Otherwise, it is prone to malfunctions such as pulling hair, powder dropping, stencil printing and transfer printing ink sticking.

In addition to the viscosities and printing suitability described above, when we consider that the viscosity of the ink is within the speed range of the printing, why does the printing adaptability have no problem when the printing speed is slow, and when the speed is increased to a certain degree, it will be If there is a slight tailing, then the color concentration becomes lighter. In the emergence of this failure, we should consider the exact definition of viscosity and stickiness of long-term neglected packaging printing inks. In this regard, before the author talks about stickiness, he first makes a statement about the definition of the viscosity of the printing ink.

The definition of viscosity

Before we introduce the difference in viscosity, we all know that: Viscosity is an important measure of the rheology of printing inks, and it is also a major indicator of ink and printing suitability. Many of the many rheological and application properties of inks are related to viscosity. However, the instruments for measuring the viscosity of printing inks are often classified into cone-plate, belt-type, shaft-type, parallel-plate, rotary-type, and small-hole-type viscometers. The term "viscosity" used to refer to the dynamic viscosity, relative viscosity, and kinematic viscosity, which were collectively referred to as the viscosity. In the 1990s, for the sake of viscosity, it simply referred to the abbreviation for "dynamic viscosity." I hereby make the following special instructions:

Dynamic viscosity: Abbreviated viscosity, symbol y, defined as (μ) = C/D, where C is the shear stress and D is the velocity convergence in the direction of the flow layer, ie, the shear stress of the fluid flow divided by Flow velocity direction Its S1 unit is Pa.sec., and it is commonly used in chemical technology. In the past, centimeters of restraint were used in centimeters. 1 centipoise = 1 millipascal second.

Relative viscosity: In the past, often mistakenly referred to as the specific viscosity, or even simply referred to as the viscosity. It is defined as the ratio of the dynamic viscosity of a fluid to the dynamic viscosity of water at temperature. It is the amount of steel without quantity, and sometimes it also increases the ratio of the dynamic viscosity of a molecular solution to the pure solution dynamic viscosity at the same temperature.

Kinematic viscosity: The symbol is V and is defined as V=y/P. Where y is the dynamic viscosity and P is its density, which is the dynamic viscosity divided by the density of the fluid. The S1 unit is m2/sec. Milliseconds/second are commonly used in chemical engineering, and centimeters and centiseconds have been used in centimeters. 1 cSt = 1 mm2/sec.

Printing ink adhesion and printing adaptability

The meaning and conditions of stickiness

The general definition of the viscosity of a packaged printing ink is the adhesion of a substance. It can also be explained as follows: at a given speed, the printing ink separates two flat surfaces of a certain unit area (they are glued together by liquids) The force. In the past, people mistakenly thought that a printing ink with a large viscosity had a large adhesion force. In fact, viscosity and viscosity are related, but it refers only to the individual viscosity of the printing ink which has a large viscosity and is occasionally large, or an extremely unstable ink viscosity under certain conditions.

For many years, ink manufacturers in China have misled some packaging and printing operators. After many years of repeated practice, it was found that: Some printing inks have large differences in viscosity, but their fastness of printing adhesion is very similar, and they cannot With high viscosity printing inks, the stickiness is also big enough to justify. The author believes that: As a technical indicator for packaging printing inks, inks should be selected based on their stickiness. This is not to say that the viscosity is not taken into account, because the size of the adhesive not only determines the quality of the gloss, adhesion, hiding power, color density, etc., but also determines the amount of printing. For this purpose, I have made detailed exchanges and descriptions on quantity and quality issues with Wang Yong, manager of Shandong Yongfei Group, and Jin Yazhang, manager of Jiangsu Nanjing, and Dibang Wang, director of Zhejiang Hangzhou.

The author has compared the inks used by Yongfei Group, for example, using the inks printed by Nanjing Ink Factory:

(1) a coat of -4 cups of ink net weight 91.7g;

(2) The ink viscosity index is 200 seconds (actually 204 seconds)/25°C. Coated -4 cups;

(3) 100 seconds/25°C after adding 1:1 thinner;

(4) The viscosity is 57 seconds/25°C when added to 1:2 dilute material;

(5) 38 seconds/25°C·coating -4 cups when added to 1:3 thinner material;

(6) 23 seconds/25°C·coating -4 cups when diluted to 1:4.

While testing the yellow ink of a printing factory in southern Jiangsu:

(1) a coat of -4 cups of ink net weight 94.3g;

(2) The ink viscosity index is 67 seconds/25°C · Coated -4 cups;

(3) 54 seconds/25°C after adding 1:1 thinner;

(4) The viscosity is 42 seconds/25°C when added to 1:2 dilute material;

(5) 31 seconds/25°C·coating -4 cups when added to 1:3 thinner material;

(6) 22 seconds/25°C·coating -4 cups when diluted to 1:4.

The authors performed the same comparison under the same conditions. As a result, the latter was disadvantageous in terms of viscosity index (and when it was added to 1:4 thinner, it was indeed close to the former), and after the printing was finished, its printing The number of out of the former is more than 7% of the former.

Viscosity representation does not mean that the viscosity is large after printing. Facts have proved that for the packaging and printing companies not only require the ink provider, but also have a certain range of viscosity, not to judge the usual ink consistency or concentration as the viscosity. The viscosity we refer to refers only to the dynamic viscosity. The ink film left on the substrate is not a solvent, but a resin, a pigment, and a filler. In a word, seeking quality can only confirm quality, while quantity can effectively control printing production costs.

Of course, in the discussion of stickiness, we should pay more attention to the mutual stickiness between ink colors. Generally speaking, the stickiness of the latter color ink cannot be greater than the previous color, otherwise it will pull down the previous color ink on the printing (often called Dyeing and other malfunctions). In order to prevent the above failures, the packaging and printing operator adds as much as possible the true solvent to the prior printing ink system when adding the ink thinner, and it is advisable to add more diluent to the printing ink system later.

The general theory of stickiness

The viscous theory of packaging printing inks is different from ink's viscosity after people's long-term practice. In theory, the viscosity of the printing ink is not only the nature of the viscosity of the ink used, but also the elastic breakage characteristics of the solid.

Through the meaning of stickiness and the conditions for identification, we have seen that stickiness is a complex situation. It is related to elasticity, adhesion properties, surface tension and other factors. It is also related to the adaptability of packaging printing. We must stick below the critical point for the viscous coefficient and the viscosity of the ink to plastic, paper, and metal inks. Otherwise, the phenomenon of stencil or paper pull, wool meshing, etc. will occur at this speed. If the printing conditions allow, then the higher the better the viscosity of the ink, so that the printed matter can be clear and complete network points, printing ink can be added more dilute material or varnish to increase the number of printed products.

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