Several important conditions for ink preservation

The so-called crust of the ink refers to: the surface layer of the packaging printing ink is in contact with the air during storage or printing due to drying at room temperature due to oxidation, penetration, volatilization, evaporation, etc., the oxidation of the vegetable oil or the volatilization of the organic solvent leads to the ink system Gel formed by polymerization and other actions. When the concentration of the printing ink increases to a certain value, its surface will be covered by a layer of molecules. At this time, even if a solvent or grease is added to reduce the concentration of the ink, the surface that has been skinned (gel) is no longer possible. Accommodate more molecules.

When the ink skinning phenomenon is serious, it will have a great impact on the stability of printing costs. According to calculations, the lighter waste 1%, and the heaviest nearly 4%. This tangible consumption adds a heavy economic burden to packaging and printing companies. Secondly, the impact on the quality of printed products cannot be ignored. When the ink skins during the printing process, the ink skin will be distributed to each link of the ink transmission under the effect of rolling, which has a great impact on the normal ink delivery. At the same time, when the ink skin adheres to the ink roller against the plate, it will Abrupt changes in the density of the graphics on the printing plate; when the ink skin is transferred to the printing plate and the blanket, it will cause ring marks on the printed product; when the ink skin adheres to the water roller, it will cause water to be transferred Unusual, dirty phenomenon; ink skin may also be directly attached to the paper surface.

From the above we can see that it is necessary to prevent and deal with the phenomenon of ink crust. So how does the crust of ink appear?

As we mentioned above, the ink skinning phenomenon is a phenomenon of oxidative filming of the connecting material in the ink. The mechanism of conjunctiva is the same as that of ink drying. It is also affected by factors such as temperature, humidity, oxygen in the air, and the content of desiccant in the ink. To put it simply, the ink skinning phenomenon is actually an oxidative conjunctival phenomenon of ink that we do not want to see (because conjunctiva occurs when we do not want the conjunctiva).

There are many factors that can cause the ink to crust, but it comes down to the following categories: the dry oil content in the ink is too high; due to temperature reasons; due to the long-term contact between the ink and the air. Below we will do some analysis.

1. The content of dry oil in the ink is too high

In general, such mistakes may occur during the process of manufacturing ink or during the printing process. Adding desiccant must be combined with printing conditions and ambient temperature to add an appropriate amount, otherwise the ink will dry (skin) when you do not want to dry. As for the use of desiccant, it will not be repeated here.

2. Due to temperature

The crust of ink caused by temperature is mainly caused by high temperature. When the temperature is too high, the activity of unsaturated molecules in the ink increases, especially the part of the surface that is in contact with air is easier to oxidize the conjunctiva under the action of oxygen. The high temperature mentioned here has the following aspects:

a) The ambient temperature is too high. According to our experience, the ink skinning phenomenon in summer is much more obvious than that in winter, and it will be more obvious if there is no air conditioning in the workshop. It is necessary to control the temperature of the working environment reasonably. Generally speaking, it is an ideal temperature to control the temperature of the workshop at about 20 ℃, which can ensure the good fluidity and transfer performance of the ink, and can control the skin of the ink A relatively low degree.

b) When the temperature on the machine (such as between the ink rollers) is too high, the ink will also cause skinning during the printing process. When the contact pressure between the ink rollers is too large, the temperature rise is more obvious. At this time, the ink is likely to form a skin on the ink fountain and the ink roller.