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The Basic Constituent
 
     Classification And Dryness Of Printing Inks

    
While technology is improving and market is developing continuously, people have more demand on printing matters, and the openness and digitalization of word and graphics processing system are becoming basic characteristic of pre-press process.
Direct plate making technology and digital printing have become the developing direction of printing and publishing industry. Commercialization of research and application of color offset printing machines, offset printing UV ink and no-water ink, re-inflame hopes of China,s printing and packaging industries to invest in offset printing machines.
While laws and regulations of environment related to printing industry is continuously achieving maturity, the most common problem met by sales people, technical service representatives and printing workers, is the dryness of coated and non-coated paper. Here we have to understand basic constituent and classification of printing ink.

1. Basic constituent of printing ink:

Printing ink:It is a mixture composed of colored pigment (such as dye), connective agent, fill-in agent and add-on agent. It can proceed in printing, and can dry on printing objects. It also has color and has certain degree of mobility and is a plasma-like colloid object.

The pigment:It is not soluble in water, as well in oil or connective agent. It is a kind of solid powder material having color.

Connective agent: it is a kind of sticky colloid fluid. Regarding its name, it serves on connection effect. Inside the ink, it is for mixing and connecting powder-state pigments together, and after rubbing and dispersion, it forms a plasma-like colloid of certain degree of mobility and stickiness.

Connective agent:It is the main component of liquid part, and determines mobility, stickiness, dryness and printing adaptability of the ink. It can be considered as the heart of the ink.

Fill-in agent:It is white, transparent, translucent or opaque powder-state material, and is also constituent of solid part of ink. It has function of filling in ink. If it is chosen appropriately, the using quantity of pigment will be reduced, cost becomes lower, and properties of ink like density and mobility can be adjusted.

Add-on agent: it is the continuation part of ink. It can also act as adding on material for ink product and serve as aiding agent to change or raise certain properties of ink, such as dryness, rubbing endurance, and so on.

 
2. Classification of printing ink:
There are a lot of types of printing inks, and the following diagram shows the major classification:

3. Dryness of printing ink:

The drying process on paper of planographic printing ink is that the ink changes from the state of high mobility colloid to solid state.

There are two indexes for balancing dryness of planographic printing ink:

One is drying speed, it refers to the ink changing from natural fluid state to semi-solid state, and it is called first-drying. The first-drying of ink is determined by chosen resin structure. The time of first-drying is very short, but it is not completely dry.

He second index is oxidation, form membrane and dryness. This refers to the complete drying in printing process, the drying time is comparatively longer, normally about 8 hours. The complete drying of ink is determined by drying agent types and quantity. In a certain range, it can be adjusted. Currently, planographic printing ink is resin-typed with comparatively high drying speed. Theoretically, it is better for faster first-dry. However, if the first-dry is too fast, it will affect color*s luster. The numeric value of luster is inversely proportional to drying speed, so a balance is required.

People always hope that ink which printed on paper can dry quickly; however, it does not dry in ink fountain.
Currently, there is about 80% of ink in the market has form membrane drying time within 16-30 hours. If the drying time is too short, it is easy for skinning on roller happens. Printing common copper plate and during long-run printing, you can choose non-skinning ink. In fact, it does not mean that ink with long form membrane drying time will avoid skinning forever. Non-skinning ink is not suitable for high-standard, but low penetrability copper plate*s short-run printing (about 12 hours for packaging printing matters proceeding), or card paper printing. It is recommended to use ink with short complete-drying time in these situations.