Several common ink adjuvants in offset printing
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In offset printing, we often encounter a variety of different printing problems, many of which are solved by adding different adjuvants to the ink. In addition, when the process conditions, substrate materials, external environmental changes and other factors change, we often improve the printing suitability of the ink by adding certain additives to the ink. Therefore, it is necessary to understand the role that different adjuvants can play in printing inks, as well as to master the methods and rules of use. In the following article we will introduce some of the more common adjuvants.
Dryness adjuster
Since we often encounter the drying properties of the ink itself in the production and the difference we hope to obtain, we often use a drying adjuster. Dryness adjusters are generally classified into two types, a drying agent and an anti-drying agent.
1. Drying agent. Dry-drying agents are commonly referred to as dry oils, and are also directly referred to as desiccants. In the production, if the printing speed is fast, the surface absorbability of the substrate is poor, and other reasons such as slow drying of the ink layer or smearing of the back surface, it is often Add an appropriate amount of dry oil to the ink.
Main ingredients of dry oil
The main components of dry oil are organic acid soaps of metals such as cobalt, manganese and lead.
Drying principle of dry oil
The principle of drying oil has not been clearly defined, and it is still widely debated. The following two are relatively convincing explanations: The first one, the ink contains dry vegetable oil, and in the dry vegetable oil, there are often some phospholipids that are easily oxidized. These substances will be dried during the drying process of the ink. It is preferentially combined with oxygen in the air, which causes the dry oil in the ink to reduce the drying speed due to "anoxia". When the dry oil is added, the metal in the dry oil is reduced to a low price, and the phospholipid is oxidized by oxygen. It has been oxidized before, and has lost the "antioxidation" effect, so it can effectively reduce the drying time of the ink. The second explanation is that it can promote the formation of free radicals. In the stage of hydroperoxide formation, since the hydroperoxide is very unstable, it will rapidly decompose under the catalytic action of cobalt to form free radicals, and cobalt ions themselves will not The change can continue to work, and the formation of an active radical will continue to polymerize.
Type of dry oil
White dry oil: Its main composition is lead, manganese, cobalt soap, which is characterized by the ability to dry the ink from the inside to the outside. The white dry oil can be used alone or in combination with red dry oil. The time of adding and drying the white dry oil should be added before the printing is started, otherwise it will be conjunctiva or gelatinized due to the long time of the addition. In addition, due to the presence of harmful metals in the dry oil, it cannot be used in the printing of food packaging.
Red dry oil: The main active ingredient of red dry oil is cobalt, which has strong drying performance. The drying process is to dry the surface from the surface and lead to the film conjunctiva on the printing machine. In addition, since the red color of the red dry oil itself has a certain influence on the hue of the ink, it is necessary to be cautious in use (see below for the specific amount).
New desiccant: Because it does not contain toxic heavy metals, it is more effective than the first two, so it is widely accepted and used.
Dry oil consumption
Through some analysis of the principle above, we will find that the role of dry oil in the drying process of the ink is to promote rather than change the nature of the ink drying. In addition, no matter which kind of explanation will explain a problem, the amount of dry oil in the ink is not increased as much as possible. When the dry oil is added to a certain extent, it will not play any benign effect, but will be dry. The emulsification of heavy metals in the oil causes the ink to be excessively emulsified, and the anti-oxidation of water particles and water film accumulated in the ink causes the ink to further dry.
So how much desiccant is added to the ink to meet the requirements? See the table below
Ink color White dry oil dosage (%) Red dry oil dosage (%)
Black 5~10 2~5
Product 5 2~5
Green yellow 3~4 1~3
Yellow 3~4 1~3
2. Anti-drying agent
Anti-drying agents are also called antioxidants. Sometimes the ambient temperature is too high, or the drying properties of the ink itself are too strong. In order to prevent the ink from oxidizing on the printing machine, the ink is transferred, and an appropriate amount of anti-drying agent is added to the ink. It has a certain retarding effect on the drying of the ink. Its main component is a strong reducing agent (hydroquinone, catechol, etc.), which can be preferentially oxidized before the ink receives oxygen. The amount of anti-drying agent should be strictly controlled below 1%, otherwise it will be harmful to printing and not beneficial. Since the use of anti-drying agents in printing is not very much, there is no excessive introduction here.
Fluidity and viscosity modifier
The fluidity modifier is an adjuvant used to adjust the fluidity, adhesion (TACK) and viscosity (VISCOSITY) of the ink.
Commonly used such adjuvants are:
1. Detachment agent. The detackifier is a paste substance whose main components are aluminum salts (such as aluminum stearate, aluminum octacarbonate), linseed oil, low viscosity alkyd resin and paraffin oil. The debonding agent is thick and loose and soft, and has no adhesiveness. The main role of the detackifier in the ink is to reduce the adhesion of the ink (TACK value) without changing its fluidity. In the process of lithographic printing and letterpress printing, if the paper is napped due to the low surface strength of the paper, poor water resistance, and excessive adhesion of the ink, and the failure of the paste, the pile rubber, etc., an appropriate amount of addition can be improved. Also note that the detackifier only changes the viscosity of the ink without changing the fluidity of the ink. When the ink has a fluidity of more than 32 mm and the viscosity is too large, the use of a paste-like debonding agent can ensure the body of the ink and keep the dots intact.
Use of debonding agent: The debonding agent should not exceed 5% in use. If it is used too much, it will form a layer of wax on the surface of the ink layer to hinder the normal transmission of ink and hinder the contact between ink and oxygen. It will reduce the cohesive force of the ink due to its own loose characteristics, and it will easily exacerbate the emulsification of the ink. This is not good for the gloss or drying speed of the ink. Therefore, the use of the debonding agent in the ink must be strictly controlled.
2. No. 6 varnish
The composition is a mixture of dry vegetable oil and high boiling petroleum solvent. The use of No. 6 varnish in the ink can simultaneously reduce the adhesion of the ink and improve the fluidity of the ink. When the drying performance of the ink roller of the machine is not good, the proper addition of the No. 6 oil can be obviously improved.
The use of No. 6 oil: There is no obvious proportional limitation on the use of No. 6 oil, and most of the use is based on the experience of the operator. However, the excessive addition of the No. 6 oil will slow the fixation of the ink on the printed matter, causing the back surface to be smeared, and the excessive penetration of the ink on the surface of the printed matter due to excessively thin ink, and surface crystallization.
3. Thinner (high boiling oil)
Its main component is a high boiling petroleum solvent. It is a mineral type varnish. The addition of ink can reduce the viscosity of the ink and improve the fluidity without affecting the fast fixing ability of the resin ink.
Use of mineral diluent: Since the mineral oil type diluent and the resin in the ink are soluble and insoluble (release), they should be gradually added under agitation to avoid resin precipitation. Generally, the thinning effect of the thinner is good, generally adding 1% can reduce a sticky unit. Note on the usage in use is the same as above.
It is a kind of varnish, and its composition is similar to the binder in the ink. Therefore, the application of varnish only changes the physical properties (fluidity) of the ink, and the role of 0# varnish is to Improve the cohesion of the ink.
When the following conditions occur, you need to add 0# varnish to the ink.
1 It is necessary to improve the fixing force of the ink on the paper surface to make the print strong and enhance the firmness;
2 control ink emulsification and overcome floating;
3 Reduce the penetration of the connecting material on the paper, prevent oil penetration and chalking, and increase the gloss of the printed product.
4 used to overcome the stacking phenomenon.
0# Use of varnish: Since 0# varnish has a large viscosity, it is often difficult to mix with ink. The thick ink should be patted thoroughly with an ink knife. Then add a small amount of ink to the varnish, then continue to pat, and mix it into the ink and stir well.
Tone conditioner
1. Dilution agent
The use of a thinner is to dilute the color of the printing ink while maintaining its adhesion. The main components are composed of aluminum stearate, dry vegetable oil, phenolic resin, beeswax, high boiling point kerosene and the like. It is a kind of grease-like transparent substance specially designed for bright resin inks. It is used as a color modifier and has excellent gloss and good printability.
The use of thinner: there is no ratio limitation of the dilution agent in the process of mixing with the ink. The specific proportion should be determined according to the color tone of the ink to be obtained. In the process of blending the extremely light ink, pay attention to the adjustment order. The ink is added to the thinner to make the blending operation more convenient and accurate.
2. Transparent oil (Weili oil)
The main components of Wei Li oil are aluminum hydroxide and polymer oil. It has good printing performance and is generally mixed with resin ink. In addition to reducing the color saturation of the ink, it can effectively reduce the problem of vitrification. Do not use more than 1/3. Do not use Wei Li oil when printing the last color. In order to avoid reducing the gloss of the ink layer.
Try to avoid using Wei Li oil in fast-drying bright ink, otherwise it will cause the ink layer to lose luster, reduce dryness, and even cause gelatinization and other defects.
3. White ink
Under normal circumstances, it is not recommended, because the white ink itself has coarser pigment particles and poor printability. It is very easy to stack rubber, paste, and emulsifie in the printing process. The light ink used in white ink is always used in printing. Very headache. But sometimes it is necessary to use some of the more special cases, such as the need for a thicker, more opaque light-colored ink layer. In order to change the printability, we also often use white ink and bright paste together, which can maintain the unique properties of white ink, improve the printability of the ink, and also improve the gloss and adhesion of the ink. benefit.
The specific use is the same as the usage of the thinner.
4. Brightening paste
The main components of the gloss paste are high-grade synthetic resin, refined dry vegetable oil, gelatin and solvent, etc., which are refined at high temperature and are transparent paste-like paste. It is mainly used for the dilution of fast-solid gloss offset inks, but it can also be used for diluting various types of oil-based resin adhesives and printing inks. It is often used as an excellent adjuvant for improving the gloss of inks.
Compared with the above auxiliary brightener, it has the following characteristics:
1 can make the ink after dilution have better printing suitability.
2 The ink diluted by the bright varnish can have the characteristics of strong gloss, moderate drying and clear dots of the printed parts.
5. White oil
White oil is a dilute agent obtained by emulsification of raw materials such as magnesium carbonate, stearic acid and polymer oil, and is a milky white translucent ink paste. The printing suitability is not good, but the biggest advantage of white oil is that the price is cheap, so white oil is often used as a thinner for low-grade light-colored offset inks in printing factories. The light-colored inks that are adjusted are sometimes printed better. The print is used to make a base.
Conclusion
Since the ink itself is configured according to scientific formula before leaving the factory, each ingredient has undergone a rigorous test. Moreover, there is a balance between the components of the ink, and the addition of foreign components is bound to break the original balance, which affects the ink quality. In the process of using ink additives, avoid blindness, and must follow the principle of “additives are added as little as possible, and can be added without adding”. It is easy to believe the advantages offered by various additives.
Of course, the right amount of scientific use of various additives can bring many benefits to printing work and print quality.
This article gives a brief introduction to the more common adjuvants in offset printing. Of course, there are many ink adjuvants in the offset printing work that can change and improve the properties of the ink to a certain extent, such as spices, anti-smudge agents, etc. Since the use of these adjuvants is limited to more specific uses, or the application has gradually disappeared, it will not be introduced here.