Analysis of Ink Properties in Inkjet Printing

Ink-jet printing is a topic that printers are currently concerned about. It is a kind of digital printing. Digital data storage images can be used to change the output content before output. It has the advantages of high speed, small amount of copy, easy combination, variable information printing, low pollution, etc. Inkjet printing has expanded the connotation of traditional printing in terms of the printing format, the diversification of ink and printing media, and now has formed a digital inkjet printing, digital proofing, digital inkjet market and so on.

Inkjet printing is a contactless, pressureless, and non-printing printing technology. The earliest development was in 1878. By 1951, Siemens patented the technology of converting liquid ink into ink droplets. There were problems and the results were poor. It was not until 1960 that it officially entered the practical stage. With the continuous development and advancement of technology, and the continuous expansion of the market, according to US IT Strategies, the total revenue of the global inkjet market (including hardware, ink-jet printing media, and ink) will exceed US$57 billion by 2009.

The color performance and high image quality of inkjet printing have satisfied most consumers, but the time for printing is still too slow, and the requirements for paper are also high. Although there are many special inkjet papers on the market, However, the prices are high, and it is difficult for general families and student populations to use them universally. Therefore, inkjet technology can be widely applied to various types of paper. This is the most pressing technology that needs to be developed now, if the special paper for special materials is to be used for parity It is not easy, so developing a new ink composition is a straightforward and effective method.

The ink used for ink-jet printing is a special-purpose ink with a moderate viscosity, and is non-toxic, stable, does not clog the nozzle, has good moisture retention, good jetting properties, and does not corrode the metal components of the head. At present, ink-jet inks are mostly dye-based inks. The ink of the ink-jet printer must have sufficient surface tension to prevent the ink from spattering when ejected. In addition, the ink must be fast-drying to prevent haziness on the paper. Therefore, the ink itself is also one of the factors that affect the print quality. The choice of suitable ink when printing, adjusting the printing parameters in order to get a satisfactory print.

First, the composition and type of inkjet inks are a very important part 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 inkjet image. The quality also determines the shape of the ink drop and the reliability of the printing system. Inkjet inks generally consist of colorants, binders, and additives. The ink binder can be water, oily materials, solvents, resins, etc. It determines the dynamic properties of the ink distribution; in inkjet inks, the binders account for 40%-90%. The colorant plays a role of color development in the ink, generally accounting for 1%-10%. The rest is called additive, which is mainly used to improve the ink viscosity, adhesion strength, thermal stability, light resistance and surface tension.

In general, there are many types of ink used in the inkjet printing process, and there are many classification methods. At present, inks can generally be classified according to their different aspects. In general, inks are classified into water-based inks, oil-based inks, solvent-based inks, and thermosetting inks according to different linking materials.

1. Water-based inks are commonly used on apertured and non-coated substrates, such as paperboard and paper, and are often used most often in the direct mail product printing and other commercial printing markets. Can also be divided into pigment type and dye type, because the pigment is insoluble in water, it will precipitate, so the pigment particles to be ground very small, to be less than 30μm, will have a better spray printing effect, or use high resolution Can cause obstruction. The pigment's weather resistance, lightfastness, wash fastness, and fastness are all very good. The advantage of the dye is that there is no problem in solubility, and there are many types of colors, and the brightness is good, but the fastness is poor.

2. Oil-based inks are best suited for printing on perforated materials because they are dried by absorption. They are formulated with vegetable oils or mineral oils. They are particularly useful in cardboard packaging applications; they are not suitable for use in closed containers. Office space because of air pollution. The colorants used can be divided into two types: pigment type and dye type. Oil-soluble type inks are characterized by fast drying, so they are more commonly used in the industry.

3. Solvent-based inks are used for a wide range of applications, from signage printing to bar code printing to outdoor advertising. The use of such inks has high economic benefits, quick drying, and can be printed on a variety of materials, especially for non-coating materials such as printing. Vinyl, silk screen, glass, paper, etc.

4.UV/EB thermosetting ink This ink is suitable for printing on various soft and rigid substrates, such as corrugated paperboard and metal foil. UV/EB inks cure faster under UV light and have stronger durability. Ideal for DOD applications such as retail display advertising, calling cards, credit cards and frequently used shopping cards. In addition to the classification of the connection materials, in practice, there are some other classification methods: According to the color materials, divided into organic dye inks, polymeric dye inks and pigment inks; if used according to the ink The different drying mechanisms can be divided into volatile inks and polymeric inks. Aqueous and non-aqueous inks use water or other solvents as the binder. Drying is accomplished by the penetration and absorption of the ink by the substrate. If ordinary copy paper or flat paper is used, the ink and its binder are absorbed together by the substrate. This absorption will reduce the color density and sharpness of the print. Thermosetting ink means that the ink is a solid at room temperature. When it is ejected from a nozzle, it is a hot melt liquid and rapidly solidifies when it reaches the surface of the substrate. This rapid solidification feature prevents the ink from spreading or penetrating into the interior of the substrate. , ensure the printing quality.

Second, choose the right ink 1. The reason that adopts the ink that the ink jet digital printing press manufacturer offers The actual production process, the manufacturer generally chooses the ink that the ink jet equipment supplier offers, in fact, this has the advantage and the disadvantage. Of course, different digital printing opportunities use different technical methods such as continuous inkjet (CIJ) and drop-on-demand (DOD). The two inks are not interchangeable, because the two technologies are completely different. The CIJ technology refers to the continuous generation of ink droplets to form an ink droplet stream, which is imaged through a deflection plate; and DOD technology, which is a digital signal generated on demand. Some ink droplets, rather than an ink stream, change the ink at will, causing ink mess. Therefore, in the production, the premise of the maximum effect of the printing press is to have a full understanding of the ink used, which needs to consider the impact of a variety of factors.

2. Selection of printing media and inks For inkjet printing, how to control the printing effect on different printing media must analyze the properties of the printing media. Taking paper as an example, due to the thermodynamic interaction between paper and ink, the capillary action of the paper, and the spread of the ink chemical composition, etc., the absorption of ink components by the paper is caused, that is, the ink penetration. Among them, the capillary action of paper is the main cause of ink penetration. Because the paper itself is a porous water-permeable structure, the ink is easily diffused inside the paper. With the increasing development of the paper surface coating process, the different distribution of the ink inside the paper leads to different ink penetration effects. Therefore, the paper for inkjet printing requires paper with a smooth surface and a certain degree of sizing. The sprayed ink evaporates and dries. The ink dots are circular, and the printed characters are clear and the graphics are beautiful. Color inkjet printing paper, preferably with a thin layer of transparent coating on the surface, can absorb ink quickly and avoid light scattering. Inkjet inks can be printed on a variety of substrates, which is a big advantage, such as fiber, wallpaper, glass, plastic, metal foil and plastic film, and of course, on various types of paper. Knowing which type of ink-jet technology is suitable is just one aspect of the problem. Also, is the substrate material coated or uncoated? Is the substrate material porous or non-porous? Does the printing material absorb water or not absorb water? How is the effect of ink on the surface of the substrate? All these will be related to the formulation of print job plans, increase production efficiency, and ultimately improve the return on investment.

3. Selection of dye inks and pigment inks From the chemical point of view, the dyes are present in a single molecular state in the ink, and the pigments are composed of a floc which is composed of numerous pigment molecules aggregated. In general, the color performance or color gamut of a dye ink is superior to that of a pigment ink. When printing on a relatively good substrate, the use of a dye ink can achieve an effect comparable to that of a silver salt photograph. However, dyestuff inks have poor stability, especially lightfastness, dark storage stability, moisture resistance, and water resistance. The reason is that individual dye molecules have very unstable chemical properties under light, moisture, and oxidation conditions. Chemical reactions are very likely to occur, causing prints to fade. Unlike dyes, pigments in pigment inks exist in a state of flocculation in which numerous pigment molecules aggregate, and therefore their stability to the environment is better.

Dye inks are also very picky on print media and often require specialized media support to achieve this. When printing on ordinary copy paper, because the copy paper is composed of criss-crossing paper fibers, the glue material is filled between them, and the proportion of hydrophilic factors in the general dye ink accounts for a large proportion due to these hydrophilic factors. The role of dye ink is very easy to infiltrate into the paper fibers, resulting in the production of smudge on ordinary copy paper, seriously affecting the final printing effect. In contrast, pigment inks are the opposite. Instead of the hydrophilic factors, a large number of water-repelling factors are used so that the ink does not penetrate into the deep layers along the fibers, but rather adheres to the surface of the paper. According to the above advantages and disadvantages, we can know that the dye ink has strong performance, colorful, uniform, high brightness levels, easy to express color, so it is particularly suitable for indoor use; pigment ink stability and durability, suitable for outdoor use .

Third, the ink-jet printing ink control In ink-jet printing, in order to ensure results, we must do a more appropriate control of the parameters of the printing ink, water-based ink, for example, the conditions for printing control are the following: 1 In order not to clog the inkjet head, it must pass through a 0.2 μm filter. 2. Sodium chloride content should be less than 100 ppm. Sodium chloride causes the dye to settle, and sodium chloride is corrosive, especially in bubble jet systems. Although the nozzles are all made of titanium, they are still corroded by sodium chloride at high temperatures. . 3. With buffer solution effect. The pH of the ink is stable and some dyes will precipitate due to changes in pH. 4. Viscosity control (1 to 5 cp). Micro Piezo Inkjet systems have a higher viscosity requirement and bubble jet systems have lower viscosity requirements. 5. Surface tension (30-60 dyne/cm). Micro Piezo Inkjet systems require lower surface tension, and bubble jet systems require higher surface tension. 6. Drying speed is just right. Too fast and easy to plug the inkjet head or break the ink, too slow to spread, so that the dot overlap is serious. 7. Shelf life. It takes up to three months, usually one year, for the ink to be manufactured from the factory to the end of the consumer's use. Generally, the ink must be able to pass through a 0.2μm filter for one year. 8. Thermal stability. The thermal stability of the dye for the bubble jet system is better because the ink of the bubble jet system is heated to a high temperature of 400[deg.] C., and if the dye does not withstand high temperatures, it will decompose or discolor.

While controlling the property parameters of the ink well, the desired printing product must be obtained when using the ink. The method used must be correct. The performance of the ink should be monitored before, during and after printing. The printing environment should be monitored. And storage conditions such as temperature, humidity, cleanliness, and air flow can all affect the performance of inkjet inks. In addition, after printing, inkjet inks may also be exposed to undesirable environments such as UV rays, ozone, adhesives, and corrosive environments. All of these factors may degrade the quality of the printed product. The type of ink may be selected as needed to ensure that both the prepress and postpress can meet the needs of the printing environment. Inkjet ink is a chemical product and it should be properly handled to ensure safety. The MSDS Material Safety Data Sheet is a guide to operations that ensures that ink storage, use, transportation, and disposal are all performed under the specification. The best equipment does not necessarily get the best prints. For ink-jet printing, choose the right ink, deeply understand the applicable range of various types of ink, adjust the ink parameters, monitor the ink change in the inkjet printing process, and control the environment of the workshop. Only in this way can the stability of production be maintained. And the quality of the product.