Why is the film gravure inseparable from solvent ink?
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Low-solvent film ink refers to the ink used on the film with a total solvent content of not more than 5%. It has attracted great attention in the design, manufacture and practical application of printing. It is the ink manufacturing and printing in recent years. Industry hotspots. Due to the versatility of gravure and film flexo ink, the flexo printing process is relatively complete. Therefore, the flexographic ink is used as the inlet to explore the design of the film ink. I want to convey the article through the article. of.
The discussion will start from the following four parts:
Why is the film gravure inseparable from solvent ink?
Why should film inks pay attention to the three general rules of solvent ink when designing?
There are several key points to be aware of when designing and manufacturing film inks!
What are the necessary characteristics of flexo inks for film flexo inks?
Today, let's take a look: Why is the film gravure inseparable from solvent ink?
The inks applied to the film are currently mainly liquid inks, and among them, solvent inks occupy an absolute core dominance. Under the current situation of increasing environmental protection pressure, it is known that solvent ink has an impact on the operator during printing, and it is polluting the atmospheric environment. The printing industry is still reluctant to give up, preferring to use RTO or RCO and other post-treatment processes to make up for it. However, it is rarely proposed to replace solvent inks with film inks. This has to be thought-provoking: What are the characteristics of solvent inks that have made the market so popular?
Through the analysis and induction of various practical cases, we found that through the basic indicators of hue, solid content, viscosity, fineness, etc., behind these successful cases, there are three important indicators in ink design. That is, solubility, dryness and surface tension.
1. Solubility
Solubility is the most important property of all liquid inks. Solvent ink requirements for solubility are mainly reflected in three problems: one is the dissolution of the ink resin; the second is the adhesion of the ink to the film; the third is the stability of the ink during storage and the resolubility during the printing process.
(1) Dissolution of ink resin
The dissolution of the ink resin itself occurs in the process of dispersing the solid resin, that is, dissolving solid resin particles such as polyurethane, polyamide or polyacrylic acid and other kinds of resins to form a polymer solution called varnish water. . Based on varnish water, ingredients such as pigments and functional additives are added, and then physically dispersed to form a uniform ink liquid in which the pigment particles are encapsulated.
In the process of ink production, the uniformity of the water is affected by the solubility, which directly determines the quality of the ink itself. The better the solubility, the more uniform the water, as long as the pigment particles are small enough, the finer the ink particles wrapped with varnish. The better the fineness of the ink, the more it can adapt to the increasingly fine printing requirements of the user. Under the current market conditions, the fineness of the gravure solvent ink can reach 5μm or less before adding low-molecular suspension such as microcrystalline wax. Even if the related additives are added, the factory fineness is only about 20μm. It is fully qualified for the 175-line dot-point requirement of the electro-engraving gravure.
(2) Adhesion of the ink to the film
The film is different from the paper, has no capillary pores formed by the fiber, and has no osmotic absorption function, so the film printing cannot promote the formation of the ink film by permeation like paper printing. Therefore, in film printing, the adhesion of ink to the film is a key indicator that the industry is very concerned about.
Printing on the film first requires the ink to react with the surface of the film. The wet ink is slightly soluble on the surface of the film, making the surface of the originally smooth film sticky, thereby establishing fine anchor points on the surface of the film. This process of establishing anchor points on the film is understood to be dissolution. The wettability of the ink on the film ensures that it establishes enough anchor points on the film, and a large number of anchor points are connected to form an ink film. The ink forms two major elements of the ink film on the film, namely solubility and wettability, and solubility is the primary.
(3) Stability of ink during storage and resolubility during printing
The stability of the solvent ink during storage and the resolubility during the printing process are important indispensable for ink solubility. Storage stability consists of two aspects, namely the storage of the original ink and the storage of residual ink. The unopened original ink has a safe storage period of 12 months, and there is no obvious delamination and agglomeration. The technical guarantee is that the solubility is unchanged. Residual inks are different. Residual inks with a lot of mixed solvents can no longer ensure reliable solubility. Therefore, no ink company is willing to guarantee the residual ink whose solubility has changed. The resolubility in the printing process is also very important. If the solvent ink is irreversible with the solvent during use, that is, the resolubility is poor, in addition to frequent printing failures, even the cleaning of the printing plate will be a big problem, which is difficult for printing companies to bear.
2. Dryness
The drying property of the solvent ink is provided by the interaction of the solvent in the ink ink and the addition of the dilution solvent in the printing process, and the drying speed of the solvent directly determines the drying speed of the ink. The solvent drying rate is calculated in terms of its evaporation rate, which is related to the boiling point and is more related to the latent heat of vaporization. The solvent with low latent heat of vaporization has good volatility, and the solvent with large latent heat of evaporation has poor volatility.
The evaporation rate of the solvent is a relative value, which is a ratio calculated based on the evaporation time of the solvent to be tested and the evaporation time of butyl acetate. This is commonly used in the industry to measure the drying performance of the solvent. The commonly used measurement and calculation methods are: evaporation rate = 90% volatilization time of the tested solvent / 90% volatilization time of butyl acetate.
According to the evaporation rate of the solvent, the drying speed of the solvent ink is controlled. The intuitive application is to control the initial dry length of the ink by the scraper fineness meter. The national gravure ink industry standard has a very detailed method for determining the initial dry length. The dryness of the ink is closely related to the initial dryness of the ink. Therefore, if it is not necessary to consciously use the pseudo-solvent in the mixed solvent to help the solvent precipitate out of the resin, it is completely possible to use the primary dry index instead of the dry indicator. It's much simpler.
3. Surface tension
The surface tension of the solvent ink covers two aspects of the ink properties, namely the leveling of the ink and the detachment properties transferred from the surface of the printing plate. The leveling of the ink is often considered to be related to the fluidity of the ink, that is, to the level of ink viscosity. In fact, leveling is a very important characteristic of the ink, that is, the performance of the ink film flowing in a wet state and rapidly forming a flat film in the process of film formation. An important physical quantity for measuring ink leveling is the surface tension in a wet state. The lower the surface tension, the better the leveling property. The surface tension of the ink depends on the characteristics of the resin used, the solvent used, and the performance and amount of surfactant used. The value can be measured by a special liquid surface tension tester, which is very intuitive.