During the printing process, occasionally streaks of printing appear or the phenomenon of light colors, this is called the failure of the ink and ink roll off, due to the ink and the filler swell in the ink system, resulting in the overall gelation of the ink. Caused.
The theoretical explanation is that the yield value of the ink is too high and the ink is too thick to be a cheese. From a practical point of view, there are too many pigments and fillers in the ink, which causes the ink to gel or cause water in the ink system during storage to cause partial flocculation.
For a long time, people used the method of installing a stirrer or other constant stirring ink ink in the ink fountain for the problem of ink swelling or gelation, and some put an iron bar in the ink fountain to push the ink to the ink fountain roller to ensure printing. The fluidity of the ink. Operators mostly use high-viscosity varnish or thinner to adjust the ink (but must be used with it), otherwise it will continue to swell. Some manufacturers dumped the ink and replaced it with a printable, water-resistant ink.
First, the bulge of ink and acid and alkali
The problem of gelation of printing inks is often encountered in the early use of oxidative drying and osmotic drying inks, and occasionally in solvent-based (volatile drying) and water-based inks. We know that the causes of gelation are complex (including the process flow of ink manufacturing, such as the addition and subsequent addition of desiccants, etc.). 'Generally after the failure, operators often do nothing. The reasons for gelation are as follows:
1. The molecular weight of the ink system is too large (the viscosity is too high);
2. There are too many solid components (even small viscosity resin binders are no exception);
3, the acid value of the ink system is too high;
4, pigments, fillers with alkaline;
5, desiccant content is too much or the order of choice of additives is not proper (such as ink production before and after production will appear two results);
6. The solvent of the ink system is especially too much quick drying agent.
From the above reasons, it can be found that the first two belong to the category of physics, which is very easy to avoid and eliminate for an experienced ink manufacturing practitioner or printing operator. The latter four reasons belong to the category of chemistry. When we explored for the latter four reasons, it was found that the temperature of the dispersion process was too high, the volatilization of the solvent, and the improper use of auxiliary additives could also cause the tendency of the ink to gel. The various phenomena that occur indicate that both the acid and alkali, as well as the so-called amphoteric solvents, resins, and neutral pigments and amphoteric pigments that do not form hydrogen-bonded aliphatic hydrocarbon solvents are involved in the gelation, that is to say: pigments When the acidity and alkalinity of the material are not compatible with the acidity and alkalinity of the binder, we can use various resins to match the acidity and alkalinity of the pigment and filler and achieve the balance or select the appropriate solvent to be compensated or improved. This is conventional. Effective remedy.
When the stoichiometric concentration reaches a certain degree, various macroscopic properties will suddenly change. From a microscopic point of view, the active molecules represented by the ink at this time began to form a poly colloid with different sizes of colloidal particles. This kind of poly colloid forms micelles or micelles and also becomes an associated colloid. An important feature of micelles is the result of their solubilizing effect, which greatly increases the solubility of originally insoluble or sparingly soluble substances, commonly known as bloating, thereby accelerating the effects of chemical reactions.
Second, eliminate the swelling, to avoid the effective way of gelatinization
In addition to the above mentioned reasons, the driers in the ink system can also directly affect the increase of the viscosity of the ink during storage and the sinking of pigments and fillers. For example, the high-viscosity alkyd resin is ground together with the basic pigment zinc oxide and driers, which will promote the gelation and swell of the ink during storage. This is due to the fact that the chromium, cobalt, and manganese should not be added during hot processing. Agent, 1% benzoic acid can reduce the bloated tendency.
Another drawback of the driers is that they can accelerate the precipitation of pigments during storage of the ink. For example, when titanium dioxide is used to make the ink, zinc naphthenate is added during grinding, and the pigment is easily precipitated to form a hard mass. Therefore, adding the driers before the pigments are grinded will result in poor ink storage, swelling, gelation, and caking at the bottom of the ink.
Over the years, according to the phenomenon of gelation, thickening, and clumping of the ink system, people have found that the hydrochloric acid pigments are reacted with soaps with higher acid values â€‹â€‹or containing free fatty acids. This is due to the aggregation of the binder material and the ink system. Inhalation of water, high pigment content, unbalanced use of binders and pigments, poor miscibility of excipients with binders and greases, and general remediation after the acid-soluble structures of polymer binders are absorbed by pigments and accelerate gelation The measures are nothing more than the following four methods:
1. When it is too thick or gelled due to the high degree of polymerization of the linking material, it is diluted with aliphatic hydrocarbons, esters, ketones, etc.;
2. The gelled ink reacted into soap is added with rosin dissolved in linoleic oil to release its high acid value material;
3. Adding folic acid metal salt in printing ink is a common method in the past;
4, ink added inorganic salt can be controlled.
According to many years of practice for the above-mentioned failures, analyzing the structure of the ink-adjusting formula and screening out new materials for commercially available anti-expansion breakers, it is believed that the improved phosphoric acid ester-fat coupling agent has excellent dispersion properties for pigments. In addition, there is a special function that can make the swollen, gelatinized ink "resurrection". For example, in the printing process, it is only necessary to add 3% to 5% anti-expansion breaker in the swelled ink, and the above failure can be controlled to restore the original structure and viscosity of the ink.
A French press, also known as a cafetiÃ¨re, ÑafetiÃ¨re Ã piston, Cafeteria, press pot, coffee press, or coffee plunger, is a coffee brewing device patented by Italian designer Attilio Calimani in 1929.
A French press works best with coffee of a coarser grind than does a drip brew coffee filter, about the consistency of kosher salt. Finer grounds, when immersed in water, have lower permeability, requiring an excessive amount of force to be applied by hand to lower the plunger and are more likely to seep through or around the perimeter of the press filter and into the coffee. Additionally, finer grounds will tend to over-extract and cause the coffee to taste bitter. Coffee is brewed by placing the ground coffee in the empty beaker and adding hot-between 93â€“96 Â°C (199â€“205 Â°F)-water, in proportions of about 30 g (1.1 oz) of coffee grounds to 500 ml (17 US fl oz) of water, more or less to taste. The brewing time is about two to four minutes. The plunger is pressed to separate the grounds and hold them at the bottom of the beaker. The mesh piston normally does not compress the coffee grounds, as most designs leave a generous space-about 30 mm (1.2 in)-below the piston in its lowest position. If the brewed coffee is allowed to remain in the beaker with the used grounds, the coffee may become astringent and bitter, though this is an effect that some users of the French press consider desirable. It is believed that the optimum time for brewing the coffee is around four minutes, and some consider the coffee spoiled after about 20 minutes. Other approaches, such as cold-brewing, require several hours of contact between the water and the grounds to achieve the desired extraction.
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