Basic knowledge of ink additives (2)

(a) The composition of the desiccant

Desiccants can generally be divided into two major categories: (1) dissolved (metal) desiccants; (2) dispersed desiccants.

In the first category, there are mainly heavy metal soaps of organic acids whose composition is organic acids and metals.

Among organic acids, linolenic acid, resin (rosin) acid, and wood pulp oleic acid are oxidizable acids and change during storage. Naphthenic acid and octacarbonic acid are relatively stable because they are saturated organic acids.

It is very important that the system (or solution) of the compound formed by metal and organic acid maintains good solubility and stability, and this has a great relationship with organic acids. Now we tend to use saturated organic acids instead of easily oxidized acids, that is from this point of view.

On the other hand, since the desiccant is easy to leach out of the ink and chemically react with the offset ink in the offset printing, thereby reducing the dryness of the ink, the selection of the organic acid in the desiccant is very important. In general, the new synthetic acids are ideal. They are easy to form organic metal bonds without making the metal leach out. The wood pulp oleic acid, naphthoic acid, etc. are relatively large because of their organic groups, and they are unlikely to form organic metals. chain. Petroleum acid (naphthoic acid, naphthenic acid) is present in crude oil, and is industrially treated with alkali to treat crude oil and then separated, acidified, and then subjected to fractionation, the composition of which varies depending on the oil source.

The main components of naphthalene acid are:

1. Saturated cyclic carboxylic acid, its general formula: CnH2n-1COOH.

2. Saturated bicyclic carboxylic acids having the general formula: CnH2n-3COOH.

3. Aliphatic carboxylic acids have the general formula: CnH2n+1COOH.

The carbocyclic ring in the saturated monocyclic carboxylic acid is a five-membered ring. The metal soap formed from naphthenic acid is relatively stable and has good solubility. The disadvantages are dark color, odor, and low metal content. Refined naphthalene acid is lighter in color.

In addition to naphthalene acid, synthetic acids containing 8 to 13 carbon atoms are also widely used for the production of desiccants. The acidity of this type of acid is relatively high, the quality is consistent, the color is light, and there is no unpleasant odor. For example, octacarbonic acid (Oetoate), namely 2-Ethyl Hexoic Acid, abbreviated as caprylic acid. In addition, there are neo-decanoic acid eodecanoate etc. Desiccants made with such acids have a relatively high metal content. Its solubility, mixability, etc. are also very good. It is more effective than naphthalene and octadecyl.

The metals used to make desiccants are roughly the following: drilling, manganese, lead, antimony, vanadium, niobium, iron, lithium (the above belongs to oxidation-oxidation polymerization catalysts); aluminum, zirconium (above belongs to the value-added dry type) Calcium, zinc, phenanthroline (above, auxiliary drying type).

Among the metals that are of general interest are cobalt, manganese, and lead.

The most active metals are cobalt, vanadium, and manganese. The activity of nickel and copper is zero. Delaying the dry metal is almost impossible. Each metal has its own unique effect, and its properties vary, in addition to its activity.

Cobalt is purple, its main function is to promote the surface oxidation, that is, the surface energy quickly forms a layer of film, so after a lot of use there will be severe dry skin, wrinkles. Therefore, drilling dry oil known as "surface dry oil" is the most powerful desiccant.

Manganese is a brown substance, and its performance is somewhat like that of a drill, but its effect is small. It can accelerate drying (oxidation) of oil and the effect of peeling is not obvious. Dryness is poor at low temperatures, often with a large amount of lead.

The oxidation of lead is poor, and its characteristics are that the layer film thickens together. So the dry oil is called "through" dry oil. The surface of the film dried with lead does not have a skin. It is less sensitive to temperature, which means that heating will not promote lead to play a greater role. Often used with manganese.

The effect of calcium is poor, and the effect is acceptable when used with cobalt. There is instability in the use of lead dry oil in some of the binders, but when using calcium dry oil, the situation is much better.

Iron is darker in color.

(b) Production of desiccant

There are roughly three ways to make desiccants, namely, melting, precipitation (of the first type of dry oil), and dispersion (of the second type of dry oil).

1, melting method.

There are many cases in which dry oil is produced by the melting process. If there is a practice of melting metal oxides in rosin, there is also the practice of melting metal oxides in linseed oil. Metal oxides are replaced by salt, linseed oil is replaced by linolenic acid, and there are also mixtures of the two.

Here are three examples for reference:

(1) Lead naphthalate. Calculate the formula ratio first

A. V. Represents the acid value of monobasic acid (mgKOH/g). Here, the acid value of naphthalic acid is set to 230, and X=243.9.

Through calculations, it can be understood that approximately 693 grams of naphthalene lead can be obtained after 223 grams of lead oxide is reacted with approximately 488 grams of naphthalic acid. The lead content is approximately 30%.

For industrial production, naphthenic acid is first installed in a pot equipped with a stirring device capable of scraping the bottom of the pot so as to prevent carbonization of the material from the bottom, and lead oxide is slowly added (the amount of the added amount is a little more than the theoretical amount calculated). After the mixture was agitated for 15 minutes, the temperature rose to 60°C due to the exothermic reaction, heating was then started, the temperature was raised to 100°C over three hours, the temperature was maintained for eight hours, and the temperature was further raised to 150°C. After three hours, the reaction was complete. You can filter out the pot. If necessary, other substances such as a solvent may also be incorporated.

(2). Pine resin lead. Lead rosinate can be manufactured by the following process: 300 kg of rosin is placed in a stainless pot and the temperature is raised to 220° C., 40 kg of lead oxide is gradually added under stirring, and the temperature is raised to 250° C. after 30 minutes when the reactants are cooled. It will be completed when it is transparent. The pan is filtered, and after cooling, it is massed as a lead rosinate, which can be dissolved in a solvent or other medium as required.

(3). Lead linoleate. Method for preparing linoleic acid lead: Heat 250 kg of linoleic acid to 110°C, slowly add 100 kg of lead oxide under stirring, and then heat up to 180-200°C.

2, precipitation method.

Precipitation method is a widely used method, but it is not easy to control, so the quality is often in and out. Here is an example for reference:

This formula is suitable for both naphthalene acid and linoleic acid.

Cobalt naphthenate industrial production method: Naphthalene acid is added into a stirred pot by calculation, and then sodium hydroxide solution is added. The reaction is almost instantaneously performed. Heat to 90° C. After the reaction is complete, filter it to remove it. Calcium naphthalate (calcium in hard water), and then heated to 100°C. Slowly add 6% sulfuric acid drilling solution under stirring until the reactants are condensed. When the cobalt naphthalate floats on the water, stop stirring and pour the water. It was washed with hot water three times to remove the water-soluble salt, heated again at 100° C., kept stirring for four to five hours, and then heated to 1150° C. over three hours to detoxify the soap. The reaction is diluted with petroleum solvent.

3, dispersion method.

The first type of dry oil is often referred to as liquid (body) dry oil and is mostly manufactured by a specialized chemical unit (factory). The second type of dry oil, commonly known as slurry dry oil, is almost all produced by the ink industry.

Liquid cobalt dry oil, also known as red dry oil, dispersion of such dry oil is commonly known as white dry oil.

Dispersed dry oils are prepared by dispersing lead borate (even lead acetate), manganese borate (or other manganese salts, manganese soaps, etc.), fatty acid cobalt (even cobalt acetate), and inorganic peroxides in a slurry with the binder. Dry oil.

In addition to cobalt, manganese, and lead metals, calcium carbonate, zinc oxide, and other substances are sometimes added to such dry oils to adjust rheological properties such as color and thinning.

Formula example:

Resin type binder (resin content 40%) 38%

Ink oil (boiling point 250-270°C) 6%

Lead Borate 46%

Manganese borate 5%

Cobalt naphthalate (4% Cobalt) 5%

The disadvantage of the dispersion type desiccant is that due to its large use of easily oxidizable type linking materials, there is a serious peeling phenomenon during storage, which brings many difficulties for storage and use. If it is stored without peeling, it can fully exert the metal's drying performance after adding it to the ink, and it has minimal influence on the color of the ink. This is an ideal desiccant.

(III) Application of Desiccant

The application of desiccant is also a complicated issue. In the application of the ink factory, there is a relatively big drawback that it will be dry and faded by pigment adsorption.

The most typical example of pigment-adsorbed dry oil is carbon black. Others, such as some lakes, especially some tannins, aluminum hydroxide lakes, etc., have relatively severe cases of adsorbed dry oils. However, some inks made with pigments (such as toluidine red, aniline gold red, etc.) are slow to dry, not because they adsorb dry oil.

Pigment adsorption dry oil is a physical role, but the dry oil failure, dry deterioration also has chemical factors, such as iron blue is. Iron blue is an iron-containing pigment. It is a positive catalyst. It is a fast drying pigment. It promotes drying (but if it contains impurities, it also causes the drying oil to decay). This is because of iron blue. Can cause ion exchange.

In general, oxidized pigments accelerate drying. Reduced pigments retard drying. However, this is not absolute. For example, zinc chromate yellow pigment retards the drying phenomenon (zinc acetate is more severe than zinc nitrate in production). Others such as water-soluble salts in pigments (or their surface adsorbents - such as various additives) can also make dry oils lose their drying effect, such as phosphate in aluminum pigments, iron salts in iron blue, lead chromate, etc. In the acetate, etc., there are cases where the metal in the dry oil fails.

In addition to the pigments, the binders also have some influence. For example, if the malic acid resin used in the dry oil binders mentioned above has the property of adsorbing dry oils, the acidity of the binders may be inappropriate. It can be soaped with metal to reduce the drying performance of dry oil, etc.

When dry oils are used in the printing industry, more problems occur. The systems that make up dry oils (such as binders), if they are hydrophilic, will have greatly reduced dryness, acidity and alkalinity of the paper, and acid in the printing solution. Such as dry oil will reduce dryness. Therefore, the dry oil itself should first have good water resistance, and the acidity of the printing paper should not be too great.

Assuming that the printing solution is stationary (not recycled) on the printing press, the acidity of the solution changes to neutrality after printing for a short time because of the metal in the ink (ie, the metal in the dry oil) and the solution. The acid reacts with a salt to produce a chemical reaction. This means that the desiccant in the ink, metal (especially cobalt), has leach into the potion. Obviously, the dryness of the ink will decrease accordingly. Therefore, adding some soluble metal salts (such as cobalt acetate) in the printing solution will help dry the ink and maintain the balance of the syrup.

The relative humidity of the printing room should not be too high, generally 65% ​​± 5% is desirable, because the humidity is too high means that the humidity of the paper is high (which reduces its absorbency, and therefore also known, printing Drugs) The amount of water can not be too large, generally do not dirty version of the principle.

When using dry oil in printing, there are also quantitative factors, breed factors, and so on. For example, under certain printing conditions (temperature, humidity in the printing room, potions, paper, ink, printing requirements, etc.), what is the most appropriate amount of dry oil added? What kind of dry oil is most suitable (for example, cobalt is added to black ink)? As the main dry oil, intaglio printing inks should use dry oil such as manganese as the main component).

In short, due to differences in the composition of the dry oil (such as the type of metal, the type of organic acid, the type of the binder, etc.) and other conditions (such as temperature, humidity, etc.), the application requirements for the oil are relatively complicated.