Study and Application of Non-Toluene Gravure Printing Ink

Keywords: cigarette packaging printing toluene gravure ink

I. Introduction

As China's economy has entered a period of rapid development, the vigorous development of the commodity packaging industry has not only promoted the printing industry, but also promoted the rapid development of the ink industry. The rise of plastic film packaging in the mid-1980s drove the further development of gravure printing and gravure inks. Gravure prints are brightly colored and of high quality and have been widely recognized by society. In the early 1990s, due to the specific social conditions in China, cigarette packaging caused widespread concern. The aesthetic effect of cigarette packaging printing is particularly high, so that both the cigarette industry and the printing industry are aiming at gravure printing. Many manufacturers who originally used offset printing cigarette packs turned to gravure printing. Many printing manufacturers introduced high-end high-speed gravure printing presses from home and abroad. Domestic printing machinery manufacturers also began to manufacture new high-speed gravure printing presses. Become the focus of competition among various printing manufacturers and ink manufacturers.

By the mid-1990s, most of the gravure inks used in printed cigarette packs were solvent inks and contained a large amount of toluene in the formulation. From the ink manufacturing point of view, toluene is a good solvent for resin binders. In the process of ink manufacture, toluene plays a very key role in the pigment wettability and the stability of the dispersed fine particle pigment in the ink system, so that the ink performance is stable and the storage period is longer. Judging from the gravure printing process, the ink system containing toluene shows good ink property on the ink roller; it also shows good fluidity and stability on the printing plate; and it prints on the coated paper, the volatilization rate of the solvent, ink The drying speed of the film, the blocking resistance of the printed matter, and the pick-up resistance are all good: When the solvent is volatilized, the content of the solvent remaining on the paper is also low, and thus the ink system containing the toluene solvent has been widely used. However, toluene poses a greater harm to human health. Ink manufacturers, printers, and other related personnel are adversely affected. Therefore, toluene-free gravure printing inks have been used at the same time as the toluene-containing inks are widely used. In the process of hard research and development.

This subject is to work hard with this goal, but on the one hand, it is technically difficult. On the other hand, it has to be approved by the cigarette pack printing factory and eventually by the cigarette factory. It needs repeated tests and tests, and it also needs to enter. After the market was tested by end users, the process of development, research, promotion and application of the toluene-free gravure ink was tortuous and long. In this paper, a toluene-containing gravure printing ink system was used as the reference standard. From the aspects of ink performance, printing performance and practical application promotion, the comparison of the toluene-free gravure printing ink system was made and it was confirmed that the system had practical application.

Second, ink performance and analog printing performance testing and comparison

The performance of toluene-free gravure printing ink system and the simulated printing performance were tested and compared with a gravure ink system containing toluene as a reference standard. The results show that the performance of the latter is superior or similar to the former.

1. Preparation of ink samples

The production process and manufacturing process of the toluene-free gravure ink system is basically the same as the current gravure ink system containing toluene, but the production workshop and operating equipment must strictly control the use of solvents such as toluene and xylene in order to avoid the production process. Mix in the ink. The production process can be simply described as: dissolution - pre-dispersion - sanding - conditioning - packaging, see Figure 1 gravure ink production process flow chart. The main process of dissolving is to dissolve the solid resin with a solvent into a liquid resin solution. The key is to control the viscosity, solid content, drying speed, gloss, transparency, and dissolution temperature of the resin solution. The pre-dispersion process is to disperse pigments with larger particles into smaller particles. It is necessary to grasp the dispersion state of the ink and the dispersion of the pigment to ensure the mixing time. The sanding process is to disperse the pre-dispersed base ink into a suitable particle state, and to control the ink temperature, the cooling temperature, the sanding speed and other indicators. The quenching and tempering process is to modulate the dispersed base ink into a desired finished ink by adding suitable additives and resins, and to control the ink viscosity, hue, concentration, gloss, fineness, drying speed, transparency and other indicators. Finally, through the appropriate filter device packaging factory, we must strictly control the content of impurities in the ink, pay attention to the same color before and after packaging. In order to prevent the volatilization of the solvent, the disperser of the gravure ink generally chooses to use a closed type ball mill and a closed type sand mill.

2. Ink performance comparison

Ink properties mainly include pigment dispersion, fineness distribution, hue, tinting strength, flowability, viscosity, light ocean, solids, storage stability, shed solubility, color mixing and so on. The following is a brief description of the comparison of its main performance. The comparison results are shown in Table 1 and the main performance comparison table of the toluene-free gravure ink system.

(1) Fineness

The sanding state and particle size of the ink will affect the transparency, concentration, and luster of the hue, and will indirectly affect the printability of the printing plate, such as wear, blocking, and the like. The fineness can be measured with a scraper fineness meter, which is used to observe the distribution density of particles, but this can only see the maximum limit of the distribution of agglutinated particles in the dispersion and cannot determine the molecular state. For more precise measurements, the size distribution of the dispersed particles can be obtained from the particle size distribution meter.

(2) Shade
The color shading was evaluated as a method for evaluating the hue, concentration, gloss, hiding, and fluidity of the ink, as compared with the standard ink. The shading method is used to determine the appearance, concentration, and gloss of the ink from the appearance of the ink, and the state of the ink (precipitation, separation, deterioration, etc.) can be confirmed. There are three specific test methods. a. The method of scraping, that is, the standard product and the test sample are dropped on a thin rectangular test paper, and immediately scraped with a scraper. A little force is applied at the beginning (called the background color), and the intensity can be weakened by the middle position (called Main color). b. The wire rod method uses the wire rod to develop color. Since the ink layer of the wire rod develops a thicker layer than a blade, this method is more suitable for scratching on the film. c. Manual color spreader method, which is a practical printing method, observes the printability, dryness, and color equivalent properties of the ink as the depth of intaglio and the number of anilox roller lines are different.

(3) Viscosity

In general, when measuring the viscosity and fluidity of an ink, we use a Zahn cup, a Brookfield rotational viscometer (mainly used to measure structural viscosity such as thixotropy), and a Corn Type rotational viscometer (the most suitable viscosity measurement for non-Newtonian fluids).

(4) Color and tinting power

At present, the naked eye judgment and the color difference meter are mainly used for testing at the same time.

(5) Gloss

With the judgment of hue, the use of scraping color bar to confirm the gloss, pay attention to observe the importance of the angle and light, using the variable angle gloss meter to digitalize the printed sample for more accurate determination.

(6) Solids

The solid content of the ink consists of non-volatile substances such as pigments, resins, waxes, etc. After decompression or evaporation of the volatile components in the thermostat, the weight of the non-volatile solids is directly weighed and expressed as a percentage.

(7) Storage stability

The storage stability of the ink and the long-term stability of the coating are the most critical features. For the storage stability test, place the ink in a container and seal it. After storing at room temperature or a constant temperature (40°C to 50°C) for a certain period of time, check the state of the ink (precipitation, separation, discoloration, etc.) and store it. The ink production scraping. Check the ink for changes in performance, printability, and film formation properties, as well as the degree of change.

3. Analog printing performance comparison

The printing performance samples refer to the actual used 80 to 250g/m2 coated paper, aluminum cardboard, white plate paper, white cardboard, etc. provided by a printing manufacturer, and printed using a manual or automatic colorimeter. μ m depth of print. The simulation printing performance mainly includes the initial dryness, the attachment fastness, the anti-blocking property, the friction resistance, the blade scraping property and the like. The following is a brief description of the comparison method of its main performance. The comparative results are shown in Table 2 and the comparison table of simulation printing performance of the toluene-free gravure ink system.