Talking about the Factors to Be Considered in Dry Oil Addition and Determination and Precautionary Measures (Part One)

introduction

The appropriate amount of ink adjustment and pairing of dry oil is an important condition for timely drying of the imprint, especially for overprinted printed matter. It involves the speed of drying of each color ink layer and directly affects the overprint of the next color. The effect of print drying was initially discussed.

The role and composition of dry oil

Dry oil commonly known as driers, mainly 402 red dry oil and No. 78 white dry oil, dry oil added to the ink can promote the drying of ink, while reducing the ink on the paper's penetration, improve the gloss of print imprinting.

The main component of dry oil is a metal salt. The metal salt is composed of an organic acid and a metal. Organic acids include acetic acid, linolenic acid, rosin acid, and naphthoic acid. Metals include cobalt, manganese, lead, zinc, iron, calcium,锶 and other metal elements.

The drying ability of dry oil depends on the activity of the metal. For example, cobalt has the best drying effect. It is dry on the surface and forms a film on the surface in a very short time. The drying time of manganese is also shorter, but it takes a long time to form the film. For lead, It is the slowest drying time for these three metals. The drying of the film is changed at the same time.

Due to the different drying methods of various metals, the drying of cobalt and manganese causes the ink film to dry from top to bottom or from the surface to the interior. The drying of the lead causes the ink film to function as a whole, and the drying of the ink must undergo oxidation and polymerization. In the two processes, cobalt, manganese, and lead are usually used as driers in different proportions.

(1) Red Dry Oil No. 402, mainly composed of cobalt naphthalate, has a strong stimulant effect, and is mainly composed of a surface oxide conjunctiva with a red color. It is generally added in red and black ink. Its ingredients:

Cobalt naphthalate (8% with cobalt) 40%
Rosin 30%

No. 6 varnish (refined linseed oil) 3%

(2) No. 78 white dry oil, mainly composed of a mixture of cobalt, manganese, lead metal salts, commonly known as mixed dry oil, with a comprehensive squeezing effect, its role is not as strong as red dry oil, but the drying effect is good, gray , If added excessively will dilute the color of the ink. Its ingredients:

Cobalt naphthalate 3% 19 resin oil 10%
Lead Borate 45% No. 15 Resin Oil 19%
Manganese borate 4% No. 5 varnish 19%
Determine the factors for dry oil addition

After the ink forms the imprint, it can rapidly solidify, but the solidification is not dry. The solidification of the imprinted ink layer after drying also depends on the absorption of the ink by the paper and the penetration of the ink into the paper, the oxidation and polymerization of the ink itself, etc. There are many factors that affect the dryness of print imprints, which should be taken into account when determining the dryness of oils.

1, the nature of the ink

A printing ink is a kind of colorant (pigment), a binder, a filler and an auxiliary material. The colorant and the like are uniformly dispersed in a binder composed of a macromolecular compound according to the printing technology and the suitability of the printing substrate. Stable suspensible colloidal substances, the ink according to the printing method is different, the ink layer on the paper surface drying methods are also different, mainly volatile drying, oxidative conjunctiva drying, permeability drying.

Different types of ink, the connection material is different, and the ink drying speed depends on the characteristics of the ink connection material, the connection material has dry vegetable oil and semi-dry vegetable oil, non-dry vegetable oil, mineral oil, volatile solvent, Synthetic resin, etc., so the ink type is different, the drying speed is inconsistent.

Commonly used type 10 offset resin inks are dry vegetable oils used as ink binders, which are better in alkali resistance, light resistance and water resistance, but can easily produce wrinkle skin and make the film layer dull and dry. Slightly sticky back.

The commonly used 8-head light fast-drying ink uses synthetic resin to act on the ink connecting material. It is fast-fixing, fast-drying, fast-filming, and the drying speed of the print is greatly accelerated. Therefore, when the ink is formulated, the dry oil of the 10-type offset resin ink is added. It's better to put more ink than quick-drying ink.

The same type of ink, due to the different colors of ink, different pigments and dyes, the drying speed is also different, the drying speed of various types of 10 resin ink can be arranged in this way, red ink, black ink, blue ink, yellow ink. Red ink dries slowly, yellow ink dries faster, and the rest is between the two. In general, dark ink with the same type of ink dry faster than light ink, which is from its own nature, but the addition of dry oil also pay attention to various factors, such as the red ink according to its own drying performance, Dry oil can add more than other inks. However, the red ink has different heat resistance, light resistance, and good quality. For red light with poor light and heat resistance, such as 05-15 pink, more dry oil, easy to fade.

2. Ink Additive Factors

In order for the ink to have good printability, it is necessary to add some appropriate amount of additives to the ink, and some additives have an effect on the drying of the ink. For example, the addition of 915 Ville oil in the ink can be achieved. Dilute the effect of the ink, but due to the fine particles, light weight, delicate texture and lubrication, it is easy to penetrate into the interior of the paper. If overdosing, the amount of paper suction reaches saturation, then the rest will hinder the difficulty of absorbing oxygen in the ink layer and make the ink layer Drying slows down. Another example is our common No. 6 varnish, which plays a dilution role in the ink and also plays a role in reducing the viscosity of the ink. Adding to the ink increases the fluidity of the ink and improves the brushing performance. It also reduces the ink. Dryness, as well as non-dry auxiliary materials such as adding and removing adhesives in the ink, these auxiliary materials will not dry themselves, and a small amount of addition will not significantly affect the drying of the imprint, but if the amount added is too large, it will also make Drying of the blot slows.

3, the nature of the paper

The paper structure has a great influence on the ink drying speed. If the paper structure is loose and the surface is rough, the ink layer printed on the surface of the paper will partially penetrate into the interior of the paper, and the connection material remaining on the surface of the paper will be reduced accordingly, and the drying speed is accelerated. If the structure of the paper is tight and the surface is smooth, the drying speed will be slowed down. Therefore, when printing copperplate paper, dry oil should be placed in a relatively large amount, and when it is printed, it is relatively less.
In addition, the acidity and alkalinity of the paper also has a direct effect on the imprinting and drying. The stronger the acidity of the paper, the longer the ink dries. According to the experiment, when the pH value of the paper is reduced from 5.5 to 4.4, the drying speed is slowed down. Times, so, acidic paper is more dry and oily than alkaline paper.

4, fountain solution concentration factor

In the PVA version, since the hydrophilic basis of the PVA plate is the inorganic salt layer, the inorganic salt layer is continuously depleted in the printing process, and the acid salt ionization is required to supplement the loss of the inorganic salt layer, while the blank part of the PS plate is an anodic oxide. Water and air are relatively stable, and there is no need to consolidate the blank parts. Therefore, the pH value of the PS plate fountain solution is greater than that of the PVA plate fountain solution. This factor must be taken into consideration when adding dry oil.

The high concentration of hydrogen ions in the dampening solution has a destructive effect on dry oil and slows the drying of the print. Therefore, when the water of the water bucket is too acidic (PH value less than 3.8), it will cause the printing ink to quit and the back of the product Easy to stick dirty. Therefore, when we use potions, we must not only consider the ability of the syrup to clean the blank part of the printing plate, but also take into account the impact on the drying of the imprint. If it is the effect of the syrup on the drying of the printing product, it cannot be mistaken for the addition of dry oil. Too little and blindly increase the dry oil, to avoid the result of printing products and dried oil products is not the result.

5, the color printing interval time factor

Color printing products are generally multi-color printing products. How long it takes for the next color printing to be printed is a factor that should be taken into account. In particular, overprinting on the background color, lack of absorption and penetration conditions, and therefore slow drying, a four-color product, if adopted For four machines, each machine prints a color sequential flow process. If the time interval is one day, then the drying time of the dry oil in the ink should be controlled in one day. If one machine is used for one printing, it is added. When putting dry oil, it is necessary to consider the length of time between two, three and four colors of India to add dry oil.

6, the factors of environmental temperature and humidity changes

With the increase of the ambient temperature, the molecular motion is accelerated and the imprinting is drying faster. On the contrary, when the temperature is lowered, the molecular motion is slowed and the imprinting is slowed down. As the temperature rises, the oxidative polymerization of the binder in the ink also increases, the drying rate also increases, and the ink itself is an exothermic reaction during the drying of the polymerization reaction, so he in turn promotes drying of the imprint.

The humidity of the environment also affects the drying of the imprint. Relative humidity is high and the amount of water in the air is increased. Oxygen activity is greatly hindered, so that the absorption of oxygen by oil molecules will be affected. In addition, when absorbing oxygen, due to the air The increase in water molecules, more or less to absorb some of the water molecules, water molecules in the ink to play a role in blocking oxygen. Therefore, the relative humidity is high, the ink drying speed is slow, the relative humidity is small, and the ink drying speed is fast. In general, under the same conditions, a 10% increase in relative humidity will double the drying time. Therefore, it is necessary to control the temperature and humidity of the workshop.

7, the ventilation conditions of the workshop

In the interior of the workshop, the ventilation condition of the printing position and the imprinting drying also have a certain relationship. The ventilation condition of the workshop is good, the air flow is fast, and there is more opportunity to provide oxygen, which creates conditions for the oxidized conjunctiva of the ink layer, so that the drying is fast. So spread the prints and print them dry.

The thickness of the imprinted ink layer, the size and water consumption of the print, the number of prints, the degree of light in the workshop, etc., all have different influences on the print and the blotting.

In view of the influence of various factors mentioned above, some need to be controlled in terms of process technology. For example, the pH of fountain solution is strictly controlled at 4 or above, and the workshop realizes “air conditioning” so that the temperature and humidity can be controlled in a stable range. Inside, strictly control the layout of water consumption ... and so on. Can not put more dry oil as the only drying method, we must realize that dry oil is driers and emulsifiers, excessive addition will cause severe emulsification of ink, blots, but slow dry, very dry, causing many printing difficulties , be sure to use it in moderation.