Analyze the causes of swelling and gelation in ink printing and how to eliminate them
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Usually, in the ink printing process, we sometimes encounter streaks or light colors in the printing. This phenomenon is called the failure of the ink and the ink roller in the industry. The cause of this failure is due to the ink. Printing, the pigment system of the ink system and the swelling of the filler cause the overall gelation of the ink.
From a theoretical point of view: the yield value of the ink is too high, the ink is too short or cheese-like. From a practical point of view: too many pigments and fillers in the ink can gel the ink or enter the ink system during storage to cause partial flocculation.
For a long time, people have been constantly stirring the ink in the ink fountain for the expansion or gelation, or installing a stirrer in the ink fountain, and also placing an iron rod on the ink of the ink fountain to push the ink to the ink fountain roller to keep the ink printed. fluidity. Most operators prefer to use medium or high viscosity varnish or thinner to adjust the ink (but this must be used as usual, otherwise it will continue to swell or gel). Some printers have dumped the ink and replaced the ink with good fluidity and water resistance before printing. Throughout the above problems, the author explores and analyzes this issue and provides insights on how to eliminate the failure.
The relationship between ink gelation and acid-base
The problem of gelation of inks is often encountered in early oil-type (oxidative drying and permeation drying) inks, and occasionally in solvent-based (volatile drying) and aqueous inks. It must be known that the cause of gelation is very complex (including the ink manufacturing process, such as the first and last addition of the drier). With the development of science, the use of new materials has enabled us to strengthen the study of scientific theories and the control of the quality of ink components. When the composition of the ink changes today, all kinds of drawbacks will appear at any time, but will be controlled. The reasons for gelation, the industry believes that there are six:
1. The resin of the ink system has a too large molecular weight (the viscosity is too high);
2. There are too many solid components (even resin binders with low viscosity);
3. The acid value of the ink system is too high;
4. Pigments and fillers are alkaline;
5. The desiccant content is too much or the order of addition is improper (such as two results before and after the production of ink);
6. The solvent of the ink system is especially fast drying solvent;
It can be seen from the above six reasons: the first two are in the field of physics, and are easily avoided and easily ruled out by an experienced ink manufacturer or package printing operator. The latter four reasons belong to the same category of chemical (reaction). We will also find out when exploring the latter four reasons; the temperature of the dispersion process is too high, the volatilization of the solvent, and the improper application of the auxiliary additive may also cause the acidification tendency of the ink. For example, a rosin resin having a molecular weight of only 330 may cause gelation, stacking, and difficulty in inking when printing a solvent-based flexible quick-drying ink using a high-pigment slot ink. In addition, attention should be paid to the advantages and disadvantages of strongly acidic pigmented carbon pigments and rosin acid values. This is sufficient to show that acid [acid is electrophilic, electron acceptor (proton donor)] base is nucleophilic, electron donor (proton acceptor), and so-called amphoteric solvent resin (both proton donated) Body, there are proton acceptors of water, alcohol, carboxylic acid and nitrocellulose, etc., followed by an aliphatic hydrocarbon solvent that does not form hydrogen, bonds, neutral pigments and amphoteric pigments, etc. The relationship has long been obvious. That is to say, when the acid-base characteristics of the pigments are not compatible with the acid-base characteristics of the binder, we can make up or improve by using a variety of resins to match the pigment and the acid-base characteristics of the filler to balance or select an appropriate solvent. This is a regular remedy.
When we explored in the chemical (reaction) category, we found that when the stoichiometric concentration is large enough to a certain value (strictly speaking, a very narrow concentration range), the macroscopic properties will suddenly change. From a microscopic point of view, the active molecules of the ink system at this time begin to associate, forming aggregates of different sizes of colloidal particles. This aggregate is called a micelle or micelle, also known as an association colloid. An important characteristic of micelles is the result of solubilization, which greatly increases the solubility of originally insoluble or slightly soluble substances - commonly known as swelling, which accelerates the action of chemical reactions, and the mechanism of its reaction is highly likely The binder, especially the pigment dispersion process, is closely related.
Method of eliminating swelling and gelation
In addition to the above mentioned reasons, the drier in the ink system can also directly affect the viscosity, increase of the ink during storage and the sinking of the pigment and filler. For example, a high viscosity alkyd resin and an alkaline pigment zinc oxide are ground together in the presence of a drier to promote gelation and swelling during storage. This is due to the reaction of free fatty acids and basic pigments during thermal processing. Therefore, when making inks with high-viscosity ink raw materials, lead, drill, manganese, and drier should not be added during the grinding process. However, the tendency to swell can be reduced after the addition of 1% benzoic acid. Another disadvantage of drier is that it accelerates the settling of the pigment during storage. For example, when the ink is made of titanium dioxide, zinc naphthenate is added during the grinding, and the pigment is easily settled to form a hard block. Therefore, adding a drier before the pigment grinding will result in poor storage of the ink, easy swelling, gelation and agglomeration.
In recent years, people have proposed various remedies in this way and around the swelling, gelation and precipitation of ink. However, the solution is often to attract people's attention after the failure. This is a passive operation method, which not only increases the production cost of the packaging and printing manufacturers and delays the time, but also brings certain processing difficulties. Over the years, according to the phenomenon of gelation, transformation, thickening and blocking of the ink system, the industry has found out that the salt-based pigment reacts with the binder with higher acid value or free fatty acid to form soap. The binder itself is gelled, the ink system absorbs moisture, the pigment content is too high, the binder and pigment used are unbalanced (inappropriate), the binder and grease are poorly miscible, and the polymer binder is acid. The dissolution of the dissolved structure by the pigment also accelerates the gelation, etc. The general exclusion methods are generally as follows:
l. When thickening or gelation due to excessive polymerization of the binder, add aliphatic hydrocarbons, esters, ketones, etc. to dilute.
2. The gelatinized ink which reacts into soap is added to the rosin and dissolved in the linoleum by using its high acid value substance.
3. The addition of a metal ruthenate salt to the ink is a commonly used method in the past.
4. Ink can be controlled by adding inorganic salts.
In view of the above-mentioned failures, the industry analyzed the structure of the ink formulation, screened out the commercially available new materials for anti-expansion and gel breaker, and concluded that: Yizheng Tianyang Chemical Plant (national inspection-free product) produced an improved phosphoric acid. In addition to the excellent dispersing properties of the pigment, the ester octanoate coupling agent has a special effect of "sudden rejuvenation" of the swelled and gelled ink. For example, in the printing process, it is only necessary to add 3-5% anti-expansion and gel breaker to the swelled ink to suppress the above-mentioned failure, restore the original structure of the ink, and return the viscosity. According to the characteristics of anti-expansion and gel-breaking agent produced by Yizheng Tianyang Chemical Plant, we only need to directly add 1.5~2.5% anti-swelling glue to the ink formulation to avoid the swelling and gelation of ink printing. . It can also be diluted with toluene or xylene one by one and then added to the ink component to be ground and dispersed together, which can greatly improve the dispersibility of the pigment and prevent the ink from swelling during production, storage and printing. Streaks or color defects caused by gelation, precipitation. At the same time, it can greatly improve the branching degree of the ink and increase the adhesion fastness of the ink film, and can reduce the baking temperature and the blowing amount of the ink or the volatile dry type (solvent type) ink, thereby effectively promoting the fluidity of the normal printing of the ink. .
The relationship between gelation and viscosity of ink
Then it is to restore the original structure of the ink, that is, to achieve the original viscosity problem. This shows that the viscosity of the ink has a lot to do with gelation. By ink viscosity is meant a physical quantity that measures the viscosity of an ink, referred to as viscosity. There are various methods for measuring the viscosity, and there are generally a capillary viscometer, a small pore viscometer, a rotary viscometer, and a rotating cone and plate viscometer.
The factors affecting viscosity are: viscosity is closely related to temperature, concentration of component particles, particle size, etc., and has little relationship with temperature and pressure. The measurement accuracy and unit of measurement of different measurement methods are different and cannot be converted to each other.
The ink is composed of an organic solvent, a binder, a pigment, an additive, a binder, and the like. When these raw materials have been determined, the degree of processing, the method, and the composition of each component have been determined, and the quality of the pigment transfer is mainly related to the printing viscosity of the ink. Practice has proved that the ink printing viscosity has a certain range (11-24S, using the Zahn viscosity cup No. 3), the greater the viscosity of the ink printing, the worse the effect of pigment transfer. Since the action of the solvent is to dissolve the resin or the additive and the auxiliary agent, the fluidity is imparted to make the pigment easy to disperse. When the printing viscosity of the ink is too large, the entire ink system is in an excessively saturated state, and the fluidity of the pigment and the like is poor, and it cannot be uniformly dispersed, but is formed into a cluster, which is easy to be piled up to form a gelatinization, a micelle, a stack, and a hair. The aggregates are swollen so that the pigment does not smoothly enter and exit the mesh. When the ink printing viscosity is too large, the pigment can not even enter the mesh at all, and it is even more difficult to transfer. This is what is commonly referred to as the plugging phenomenon. Therefore, we only need to make the colloidal system composed of resin, pigment and other organic solvents not in an excessively saturated state, but in a saturated state or a non-saturated state, so that pigments and the like can be well dispersed therein to form a uniform and fine colloidal system. So that the pigment enters and exits the mesh smoothly, and the problem of failure can be solved. Some ink manufacturers recommend ink printing viscosity between 15 and 18 seconds (Zahn viscosity cup No. 3). However, in practice, especially in high-speed gravure printing machines (printing speed of 100 ~ 260m / min), in order to ensure a good transfer effect, but also for a long time printing, improve efficiency, ink printing viscosity is generally 11 ~ 15S ( Look for the ideal state point between the Zahn Viscosity Cup No. 3).
However, if the ink printing viscosity is too small, it means that the organic solvent content in the ink is large, and the components such as resin and pigment are relatively small, so that a smooth film layer cannot be formed when dried, and the printed product will be whitened and become dull. Light, lack of luster. Therefore, if the printed product needs to have a good gloss, it is generally considered to use a larger ink printing viscosity (13 to 19S Zahn viscosity cup No. 3).
At the same time, under the normal ambient humidity, the ink printing viscosity is above 16S (Cahn viscosity cup No. 3), and static electricity generally does not occur. The ink printing viscosity is below 16S (Zahn viscosity cup No. 3). As the viscosity becomes smaller, electrostatic phenomena such as whisker, streak, edge repulsion, flying ink, poor transfer, and extremely irregular water stains will follow. It happened and aggravated.
In view of the above reasons, industry experts believe that the ideal state of ink printing viscosity is generally found between 11 and 17S (Zahn viscosity cup No. 3). If static electricity is present in this range, static electricity can be installed by using a static elimination brush or an antistatic agent to promote the normal printing fluidity. Prevent swelling, gelatinization, ensure the quality of printed products, improve efficiency and yield, and create more benefits.