A preliminary discussion on the influence of the h

2022-08-22
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A preliminary discussion on the influence of dry oil on the drying of printed matter (Part 1)

Introduction

the appropriate addition of dry oil to ink blending is an important condition for the timely drying of imprints, especially for overprint and color overlay printed matter, it involves the drying speed of each color ink layer, which directly affects the overprint of the next color. Now a preliminary discussion is made on the influence of dry oil on the drying of printed matter

function and composition of dry oil

dry oil is commonly known as drier, mainly including No. 402 red dry oil and No. 78 white dry oil. Adding dry oil to the ink can promote the drying of the printing ink, reduce the penetration of the ink into the paper, and improve the gloss of the print imprint

dry oil is mainly composed of metal salts, which are composed of organic acids and metals. Organic acids include acetic acid, linolenic acid, rosin acid, naphthenic acid, etc., and metals include cobalt, manganese, lead, zinc, iron, calcium, strontium and other metal elements

the drying ability of dry oil depends on the activity of metal. For example, cobalt has the best drying effect. It is surface drying, and a film can be formed on the surface in a very short time; The drying time of manganese is also short, but it takes a long time to form skin film; For lead, it is the slowest drying time of these three metals, and its film drying changes up and down at the same time

due to the different drying methods of various metals, the drying of cobalt and manganese makes the ink film dry from top to bottom or from the surface to the interior, the drying of lead makes the ink film work as a whole, and the drying of ink must go through two processes of oxidation and polymerization, so cobalt, manganese and lead are usually mixed in different proportions as drying agents

(1) No. 402 red drying oil, mainly composed of cobalt naphthenate, has a strong drying effect, and the surface is mainly oxidized conjunctiva, with a red color. It is generally added in red ink and black ink. Tensile test (stress-strain test) 1. Generally, the two ends of the material sample are clamped on two fixtures with a certain distance between them. Its composition:

cobalt naphthenate (containing 8% cobalt)

rosin 30%

No. 6 inking oil (refined linseed oil) 3%

(2) No. 78 white drying oil, which is mainly composed of a mixture of metal salts of cobalt, manganese and lead, commonly known as mixed drying oil, has a comprehensive drying effect, and its effect is not as strong as that of red drying oil, However, the drying effect is good, which is grayish white. If excessive addition will dilute the color of the ink. Its ingredients:

cobalt naphthenate 3% No. 19 resin oil 1, then unplug the power 0%

lead borate 45% No. 15 resin oil 19%

manganese borate 4% No. 5 inking oil 19%

factors that should be considered in determining the amount of dry oil

after the ink forms an impression, it can solidify rapidly, but the solidification is not dry. The formation of solid after the ink layer is dried 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... Therefore, there are many factors that affect the drying of print imprinting, which should be considered when determining the amount of dry oil

1. Factors of ink properties

printing ink is a stable suspended colloidal substance formed by evenly dispersing Colorants (pigments), binders, fillers and auxiliary materials in the binders composed of polymer compounds according to the suitability requirements of printing technology and printing substrate materials. According to the different printing methods, the ink layer has different drying methods on the paper, mainly volatile drying, Oxidation conjunctiva drying, permeability drying

different types of inks have different connecting materials, and the drying speed of inks depends largely on the characteristics of ink connecting materials. Connecting materials include dry vegetable oil and semi dry vegetable oil, non dry vegetable oil, mineral oil, volatile solvent, synthetic resin, etc., so the drying speed is inconsistent with different types of inks

the commonly used type 10 offset resin ink uses dry vegetable oil as the binder of the ink, which has good alkaline resistance, light resistance and water resistance, but it is easy to wrinkle and make the film dull, and the film is slightly tacky after drying

the commonly used 8-prefix bright and fast drying ink uses synthetic resin as the ink connecting material, which has the advantages of fast fixation, fast drying, fast conjunctiva, and greatly accelerated imprint drying. Therefore, when mixing ink, the dry oil of type 10 offset resin ink is put more than that of 8-prefix bright and fast drying ink

the drying speed of the same type of ink is also different due to the different colors of the ink, pigments and dyes. The drying speed of 10 resin inks of various colors can be arranged in this way, including red ink, black ink, blue ink and yellow ink. Red ink dries slowly, yellow ink dries faster, and the rest is between the two. Generally speaking, the same type of ink, dark ink dries faster than light ink, which is from its own nature, but the addition of dry oil should also pay attention to various factors. For example, according to the drying performance of red ink, dry oil can be added more than other inks. However, red ink is also different in heat resistance, light resistance and performance. Red ink with poor light resistance and heat resistance, such as peach red, is easy to fade with more dry oil

2. Factors of ink additives

in order to make the ink have good printability, it is necessary to add an appropriate amount of additives to the ink, and some additives have an impact on the drying of the ink. For example, adding 915 Weili oil to the ink can dilute the ink, but because of the fine particles, light specific gravity, fine texture and lubrication, it is easy to penetrate into the interior of the paper. If it is added too much, the suction of the paper will reach saturation, Then the rest will hinder the difficulty of oxygen absorption of the ink layer and slow down the drying of the ink layer. Another example is our common No.6 inking oil, which plays a dilution role in the ink and also plays a role in reducing the viscosity of the ink. After being added to the ink, it increases the fluidity and brushing ability of the ink, and also reduces the dryness of the ink. In addition, non drying auxiliary materials such as adhesive are added to the ink. These auxiliary materials themselves will not dry. A small amount of addition will not significantly affect the drying of the imprint, but if the amount is too large, It will also slow down the drying of the imprint

3. Factors of paper properties

paper structure has a great influence on the drying speed of ink. If the paper structure is loose and the surface is rough, part of the ink layer printed on the paper surface will penetrate into the paper, and the connecting material left on the paper surface will be reduced accordingly, so the drying speed will be accelerated. If the paper structure is tight and the surface is smooth, the drying speed will be slowed down, so we should put more drying oil when printing coated paper, Put less offset paper when printing

in addition, the acidity and alkalinity of the paper also has a direct impact on the imprinting and drying. The stronger the acidity of the paper, the longer the drying time of the ink. According to the experiment, when the pH value of the paper is reduced from 5.5 to 4.4, the drying speed will be slowed down by three times. Therefore, the acid paper should properly put more drying oil than the alkaline paper

4. Factor of fountain solution concentration

when printing PVA version, because the hydrophilic basis of PVA version is inorganic salt layer, which is constantly lost in the printing process, acid ionization is needed to supplement the lost inorganic salt layer, while the blank part of PS version is anodic oxide, which is relatively stable to the ratio of water and air, and there is no need to consolidate the blank part, so the pH value of PS version fountain solution is greater than that of PVA version fountain solution, This factor should be taken into account when adding and discharging dry oil

the hydrogen ion concentration in the fountain solution is high, which has a destructive effect on the dry oil and slows down the drying of the imprint. Therefore, when the water bucket potion is too acidic (pH value is less than 3.8), the printing ink will not dry, and the back of the product is easy to be sticky and dirty. Therefore, when we use the potion, we should not only consider the cleaning ability of the Potion on the blank part of the printing plate, but also consider the impact on the drying of the imprint. If it is the impact of the Potion on the drying of the print, we cannot mistakenly think that it is the addition of too little dry oil and blindly increase the dry oil, so as to avoid the result that the print is not dry and the oil print is not dry

5. The factor of the interval time of laminated printing pieces

color printing products are generally multi-color products. How long the interval time of next color printing should be considered, especially on the background color, there is a lack of absorption and penetration conditions, so the drying is slow. If a four-color product is used, if four machines are used, each machine prints a flow of color sequence, Jean Claude Steinmetz, chairman of the China Europe automotive materials Commission (apimc), Cao Du, executive chairman of ialta/Vice President of Chang'an Automotive Engineering Research Institute, presided over the launching ceremony of the selection of the ialta (China) automotive lightweight green technology innovation award. If the time interval is one day, the drying time of adding dry oil to the ink should be controlled within one day. If one machine is used to complete the printing at one time, the drying oil should be added and discharged taking into account the length of time between printing two, three and four colors

6. Factors of environmental temperature and humidity changes

with the increase of ambient temperature, molecular motion accelerates and imprinting drying accelerates. On the contrary, when the temperature decreases, molecular motion slows down and imprinting drying slows down. As the temperature increases, the oxidation polymerization reaction of the binder in the ink also increases, and the drying speed also accelerates. The ink itself is an exothermic reaction in the drying process of the polymerization reaction, so it in turn promotes the drying of the imprint

environmental humidity also has an impact on imprinting drying. With high relative humidity, water molecules in the air increase, and the activity of oxygen is greatly hindered, so that the absorption of oxygen by oil molecules will be affected. In addition, when absorbing oxygen, due to the increase of water molecules in the air, or more or gradually realize the extension to the upstream new material field and downstream strategic emerging industries, it is less necessary to absorb some water molecules, which plays an oxygen blocking role in the ink. Therefore, when the relative humidity is high, the ink drying speed is slow, and when the relative humidity is low, the ink drying speed is fast. Generally speaking, under the same conditions, if the relative humidity increases by 10%, the drying time will be doubled. Therefore, it is necessary to control the temperature and humidity of the workshop

7. Factors of workshop ventilation conditions

in the workshop, the ventilation conditions of the placement position of the printing pieces also have a certain relationship with the imprint drying. The workshop has good ventilation conditions, the air flow is fast, and there are more opportunities to provide oxygen, creating conditions for the oxidation conjunctiva of the ink layer, so the drying is fast, so spreading the printing pieces is conducive to the imprint drying

the thickness of the imprinting ink layer, the size and water consumption of the printing pieces, the number of printing pieces, the illumination level of the workshop... Also have different effects on the printing and imprinting drying to varying degrees

to sum up, some factors need to be controlled in technology, such as strictly controlling the pH value of the fountain solution above 4, realizing "air conditioning" in the workshop so that the temperature and humidity can be controlled within a stable range, and strictly controlling the water consumption of the layout. We should not add more dry oil as the only way to dry. We should realize that dry oil is both a drier and an emulsifier. Excessive addition will cause serious emulsification of the ink, and the imprint will dry slowly instead, even if it does not dry, resulting in many printing difficulties. We must use it appropriately

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