Analysis of ink selection in inkjet printing proce

Ink jet printing (ink-jet printing) is a topic that the printing industry is currently concerned about. It is a kind of digital printing. Using digital data to store images, it can arbitrarily change its output content before output. Therefore, it has the advantages of high speed, a small amount of replication, easy combination, variable information printing, low pollution and so on. Ink jet printing has expanded the connotation of traditional printing with the diversification of printing format, ink and printing media. At present, digital ink jet printing, digital proofing, digital ink jet printing market and so on have been formed

inkjet printing is a non-contact, pressure-free and plate free printing technology. Its earliest development was in 1878. In 1951, Siemens applied for a patent for the technology of transforming liquid ink into ink droplets. At that time, due to the problems of needle and ink, the effect was poor, and it did not officially enter the practical stage until 1960. With the continuous development and progress of technology and the continuous expansion of the market, according to the prediction of American rategies company, the total revenue of the global inkjet market (including hardware, inkjet printing media and ink) will exceed $57billion by 2009

the color performance and high image quality of inkjet printing have satisfied most consumers, but the printing time is still too slow, and the requirements for paper are also very high. Although there are many inkjet special paper on the market, the price is high, which is difficult to be widely used by ordinary families and student groups. Therefore, making inkjet technology widely applicable to all kinds of paper is the most urgent technology to be developed now, It is not easy to make special paper with special materials affordable, so developing new ink components is a direct and effective way

the ink used for ink-jet printing is a special ink with moderate viscosity, which has the properties of non-toxic, stable, non blocking the nozzle, good moisture retention, good sprayability, and no corrosion to the metal components of the nozzle. At present, most ink-jet inks are dye inks. The inks of ink-jet printers must have sufficient surface tension to prevent the ink from splashing out when ejected. In addition, the ink must be fast drying to prevent blooming on the paper. Therefore, the ink itself is also one of the factors affecting the printing quality. Only by choosing the right ink and adjusting the printing parameters can we get satisfactory prints

I. composition and type of inkjet inks

inks are a very key component of inkjet printing. The development of inkjet inks also explains the development of inkjet printing technology to a certain extent, because inks not only determine the quality of inkjet images, but also determine the shape of ink droplets and the reliability of printing systems. Inkjet inks are generally composed of pigments, binders and additives. Ink binders can be water, oily substances, solvents, resins, etc., which determine the dynamic properties of ink distribution; In inkjet inks, binders account for 40% - 90%. Pigments mainly play a role in color rendering in inks, generally accounting for 1%-10%. The rest are called additives, which are mainly used to improve the viscosity, adhesion strength, thermal stability, light resistance and surface tension of the ink

generally speaking, there are many kinds of inks and classification methods used in inkjet printing process. At present, it can be generally classified from the different properties of inks. Generally, inks are divided into water-based inks, oil-based inks, solvent-based inks and thermosetting inks according to different binders

1. Water based inks

are usually used on perforated and uncoated substrate materials, such as cardboard and paper, and are also often used in the printing of direct mail products and other commercial printing markets. It can also be divided into pigment type and dye type. Because the pigment is insoluble in water, it will precipitate. Therefore, the pigment particles need to be ground very small to less than 30 m to have a better printing effect. Otherwise, it is easy to cause blockage when using high resolution. The pigment itself has excellent weatherability, lightfastness, washing fastness and wear fastness. The advantage of dyes is that there is no problem with solubility, and there are many kinds of colors, with good brightness, but poor fastness

2. Oil based inks

are most suitable for printing on materials with holes, because they are dried by absorption. Their formulations include vegetable oil or mineral oil, which is particularly prominent in the field of paperboard packaging; It is not suitable for use in closed office space, because it will cause air pollution

the pigments used can be divided into pigment type and dye type. Oil soluble inks are characterized by fast drying, so they are commonly used in industry

3. Solvent based ink

has a wide range of uses, from label printing to bar code printing to outdoor advertising. Using this ink, it has high economic benefits and can be printed on a variety of materials. It is especially suitable for the printing of non coated materials, such as vinyl, silk, glass and paper

thermosetting ink

this ink is suitable for printing on various soft and hard substrate materials, such as corrugated board and metal foil. Uv/eb ink solidifies faster and has strong durability under the action of UV light. It is very suitable for DOD applications, such as retail display advertising, cards, credit cards and frequently used shopping cards

in addition to classification based on connecting materials, there are other classification methods in practice: according to color materials, they are divided into organic dye inks, polymeric dye inks and pigment inks; According to the different drying mechanism used by the ink, the ink can be divided into volatile ink and polymeric ink. Water based and non-aqueous inks use water or other solvents as binders, and their drying is completed by the substrate 1, which must pay attention to the penetration and absorption of the ink by measuring the details. If ordinary copy paper or flat paper is used, the ink and its binders are absorbed by the substrate together, and this absorption will reduce the color density and clarity of the print. Thermosetting ink means that this kind of ink is a solid at room temperature. When it is ejected from the nozzle, it is a hot melt liquid, which solidifies rapidly when it reaches the surface of the substrate. This rapid solidification feature can prevent the ink from diffusing or penetrating into the substrate, ensuring the printing quality

II. Choose the appropriate ink

1 In the actual production process, producers generally choose inks provided by inkjet equipment suppliers. In fact, doing so has both advantages and disadvantages. Of course, different digital printing opportunities use different technical methods, such as continuous inkjet (CIJ) and on-demand inkjet (DoD). These two inks cannot be replaced each other, because the two technologies are completely different. CIJ technology refers to the continuous generation of ink droplets, forming an ink droplet flow, which is imaged through a deflection plate; DOD technology is a digital signal that generates some ink drops as needed, rather than an ink flow. Changing the ink at will will will inevitably lead to chaos in ink production. Therefore, in production, the premise of giving full play to the maximum effect of the printing machine is to have a full understanding of the ink used, which needs to consider the influence of many factors

2. Selection of substrate and ink

for inkjet printing, how to control the printing effect on different substrate media, we must analyze the performance of substrate. Taking paper as an example, due to the thermodynamic interaction between paper and ink, the capillarity of paper, and the diffusion of ink chemical components, the absorption of ink components by paper, that is, ink penetration. Among them, the capillary effect of paper is the main reason for ink penetration. Because the paper itself is a porous water seepage structure, the ink is easy to diffuse inside the paper. With the development of paper surface coating technology, the different distribution of ink in the paper leads to different ink penetration effects. Therefore, the paper for ink-jet printing requires that the surface is smooth and has a certain degree of sizing. The ink sprayed is evaporated and dried, the ink dot is circular, and the printed handwriting is clear and the graphics are beautiful. For color inkjet printing paper, it is best to have a very thin transparent coating on the surface, which can not only absorb ink quickly, but also avoid light scattering

inkjet ink can be printed on a variety of printing media, which is its major advantage, such as fiber, wallpaper, glass, plastic, metal foil and plastic film, of course, it can also be used on various types of paper. Knowing which inkjet technology is suitable for what type of materials is only one aspect of the problem. In addition, is the substrate coated or uncoated? Is the substrate porous or non porous? Does the printing material absorb water or not? What is the effect of the ink on the surface of the substrate? These will be related to the formulation of printing operation plan, improving production efficiency, and ultimately improving the return on investment

3. Selection of dye inks and pigment inks

from a chemical point of view, dyes exist in a single molecular state in inks, while pigments are composed of flocs formed by the aggregation of countless pigment molecules

in general, the color performance or gamut of dye inks is better than that of pigment inks. When printing on high-quality substrates, the use of dye inks can achieve an effect comparable to the quality of silver salt photos. However, the stability of dye inks is poor, "she added, especially light resistance, dark storage stability, moisture resistance and water resistance. The reason is that the chemical properties of a single dye molecule are very unstable under the conditions of light, moisture and oxidation, which is prone to chemical reactions and cause the fading of printed matter. Unlike dyes, pigments in pigment inks exist in the state of flocs gathered by countless pigment molecules, so their impact on the environment shows better stability

dye inks are also very picky about printing media, which often requires special media support to achieve. When printing on ordinary copy paper, because the copy paper is composed of crisscross paper fibers filled with colloidal substances, and the hydrophilic factors in general dye ink account for a large proportion, due to the role of these hydrophilic factors, dye ink is easy to penetrate along the paper fiber dimension, resulting in halo on ordinary copy paper, which seriously affects the final printing effect. On the contrary, pigment ink is replaced by a large number of water repellent factors, so that the ink will not penetrate into the deep layer along the fiber, but adhere to the surface of the paper

according to the above respective advantages and disadvantages, we can know that dye inks have strong expressive ability, bright and uniform colors, high brightness level, and are easy to express colors, so they are especially suitable for indoor use; Pigment ink has good stability and durability, and is suitable for outdoor use

III. ink control in ink-jet printing

in order to ensure the results of ink-jet printing, it is necessary to properly control the parameters of printing ink. Taking water-based ink as an example, the control conditions during printing are as follows:

1 In order not to block the inkjet head, it must pass through the 0.2 M filter

2. The content of sodium chloride must be less than 100ppm. Sodium chloride will make the dye settle down, and sodium chloride is corrosive, especially in the bubble inkjet system, it is easy to corrode the nozzle. Although the nozzle is made of titanium metal, it will still be corroded by sodium chloride at high temperature

3. It has the effect of buffer solution. The pH value of ink should be stable, and some dyes will precipitate due to the change of pH value

4. Viscosity control (1 ~ 5CP). Micro pressure EFI