Environment and safety in flexographic printing
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This paper has made a detailed analysis of the main processes and materials in flexographic printing in terms of printing environment and safety, and proposed specific methods for controlling environmental pollution factors and improving the printing environment.
Green environmental protection has become the development theme of the new century. The problem of greening in modern printing has become a major problem that hinders the sustainable development of the printing industry. It is imperative to start green projects, develop green products, and adapt to environmental requirements. With the emergence of various green products, it will inevitably require better green packaging and more practical green printing materials and corresponding printing methods. Flexographic printing is in line with the needs of the times and is increasingly becoming the preferred green printing process at home and abroad.
Flexographic printing, formerly known as "aniline printing", is named after the printing of volatile inks made with aniline dyes. Because aniline is toxic, its printing range is greatly limited. With the continuous development of powder flexographic printing technology and the increasing scope of application, as well as the promotion of non-toxic, non-residual submersible, environmentally friendly water-based inks, Uv oil and drunken oil, it adapts to environmental protection and green packaging. Requirements, so it can develop rapidly. Although flexographic printing greatly reduces environmental pollution compared to other printing methods, it is only relatively in the flexo printing process, no matter how advanced technology, process and materials are used, it is impossible to Complete, non-polluting. Therefore, to achieve further greening of flexographic printing, in addition to the pursuit of perfection in materials and processes, it is more necessary for flexographic operators and managers to make greater efforts in practice to reduce environmental pollution. Several important factors affecting the environment in flexographic printing are discussed below.
Environmental impact factors in the plate making process
Development process
An important aspect of the environment that affects the plate making process is the application of the developer. The flexible plate has undergone a development process from a rubber plate to a photosensitive resin plate, and it has been widely used due to its excellent characteristics. The flexographic rinsing is done in a special stenciling machine. The developing solution mostly uses a hydrocarbon solvent (trinitroethylene) as the main solvent, but the tris-ethylene is toxic, and its volatility is very strong. Note that the tertiary ethylene vapor in the air cannot exceed the poisoning limit. In addition, when the three atmospheres of ethylene coexist in the presence of light, air, and moisture, they decompose to produce harmful atmospheric hydrogen acid gas, causing metal corrosion. Therefore, in the process of use, there must be special cleaning equipment. The equipment itself can be recycled for recycling and is preferably in a closed form. A better approach is to develop a solvent with less side effects instead of tertiary ethylene.
2. Debonding process
De-bonding is the use of light or chemical methods to drill the layout. The purpose is to remove the drillability of the surface of the plate and enhance the ability of the powder.
1 chemical method
The method comprises the following steps: immersing the dried printing plate in a good drilling solution of the matching dish for chemical treatment, drilling and grading treatment (aqueous bleaching powder) and australation treatment (hydrochloric acid and aqueous solution of australis), it is obvious that the two The solution is extremely tolerant to the environment, so in the process of drilling, this method has gradually not taken for people.
2 illumination method
This is a commonly used method, which is accomplished by irradiating the solution in Australia with ultraviolet c (UV-c light source). Compared with the first method, the environmental pollution caused by the illumination method is much lighter, but it should be noted that the solution after the short-wave radiation in the illumination method is harmful to the environment, and the waste liquid should be properly disposed.
At the LabeExpo in Chicago in September 2000, DuPont introduced the Sally Express System, a fully digital dry plate making system. The essence is a hot-processed version, and the entire process is completely dry.
Since no solvent is required, it completely avoids environmental pollution problems caused by solvents. In addition, it also greatly reduces the plate making time, and the processing process is also faster without drying.
Environmental factors in ink applications
At present, oil is the biggest source of pollution in the printing industry. The annual production of oil in the world has reached 3 million tons. Global emissions of VOCs (organic volatiles) caused by inks have reached hundreds of thousands of tons per year. These organic volatiles can form a more serious greenhouse effect than cO2, and the formation of oxides and photochemical smog under the irradiation of sunlight seriously pollutes the atmospheric environment, which has caused widespread concern in various fields. Among the various printing methods, only the eco-friendly green printing material-water-based ink has been widely used in flexographic printing. The Uv ink and the drunk-dissolving ink mainly introduce the first two.
Water-based ink
The biggest feature of water-based inks is that it significantly reduces the emission of voc (organic volatiles), thereby preventing air pollution from improving the printing environment and contributing to worker health. It can completely eliminate the harm of certain toxic and harmful substances in solvent-based inks to the human body and the pollution of packaging products, and improve the overall environmental quality. It is especially suitable for packaging and printing products with strict sanitary conditions such as food, beverages and medicines. In addition, it not only reduces the risk of fire and stagnation caused by static electricity and flammable solvents, but also reduces the solvent odor remaining on the printed surface.
As people's call for environmental protection is getting higher and higher, the status of water-based inks will become more and more important, and its use will inevitably become more extensive. Therefore, we must control the characteristics of water-based inks more strictly to minimize environmental pollution. Although the water-based ink significantly reduces the placement of the VOC, we hope to control this emission f to a lower level. In the air cleaning program implemented in California a few years ago, the content of organic volatiles in aqueous inks is required to be no more than 3%. In addition, many users and manufacturers have restrictions and requirements for heavy metal containing f in water-based inks. That is to say, in the formulation of water-based inks, it is necessary to correctly select pigments to eliminate pigments with high levels of heavy metal ions.
2.Uv ink
Uv radiation curing products (including Uv inks and Uv varnishes) are known as “green industrial new technologies for the 21st century” for their high efficiency, energy saving, solvent-free emission, no environmental pollution and excellent product performance. Their safety has been The US Environmental Protection Agency agrees. In the past 10 years, the application of UV oil and UV coatings has become increasingly popular. According to statistics, the flexographic printing UV ink used by the United States in 2001 has reached 3,500 tons.
UV ink is not only a solvent-free safety oil, but also has many excellent properties. For example, it is not easy to paste, clear dots, bright and bright ink, excellent chemical resistance, and low dosage. The promotion and application of UV oil is not only beneficial to environmental protection, but also conducive to the improvement of the quality of flexo printing products, and promotes the further development of flexographic printing technology.
From the perspective of environmental protection, UV ink is indeed a very ideal ink. It should be noted that most UV products can be considered skin irritation before they are dried. However, due to their low volatility, these products can reduce such problems if they maintain the habit of wearing skin care gloves and eye protection during operation. In addition, it is necessary to provide subsequent processing of the exhaust system because the old type of ultraviolet ink emits oxygen.
The environmental impact of anilox roller cleaning
In flexographic printing, the anilox roll is an extremely important unit in the ink transfer process. Its surface is covered with extremely fine cells, through which the ink is transferred, and the ink clogs are transparent. A very headache in printing. Usually, the mesh plugging is caused by the blockage of the oil-filled mesh of the anilox roller during the working process. Therefore, the anilox roller should be cleaned in a timely manner during the printing process.
Cleaning methods generally have the following types:
1. Strong corrosion chemical cleaning method
Apply a corrosive cleaning agent (usually an alkaline solution) evenly on the surface of the anilox roll. If necessary, wrap a layer of plastic on the surface of the anilox roll to prevent the liquid from evaporating. The anilox roll is ablated for 1-48 hours. After the ink is fully softened, the anilox roller is cleaned by a manual cleaning method using water or an alcohol solution (not using an acidic solution such as acetic acid). Such a cleaning method has a good cleaning effect, but has a certain corrosive effect on the anilox roller and causes environmental pollution.
2. Jet cleaning method
Spraying the baking soda softening cleaning medium onto the surface of the anilox roll breaks the solidified ink for cleaning purposes. Baking soda is easy to dissolve and non-toxic. When it collides with other substances, its crystals are easily broken and will not cause damage to the surface of the anilox roll and the wall of the ink. Therefore, this cleaning method has a good cleaning effect and has a promotion and use price.
3. Ultrasonic washing method
The retort roller is immersed in an ultrasonic cleaning bath filled with a chemical cleaning solution. When cleaning, the anilox roller slowly rotates. The frequency conversion device that can transmit high-frequency sound waves in the pool starts to work, causing the solution to vibrate and generate bubbles, thereby causing continuous inward explosion. The explosive force ejects the ink from the cell and flows away with the cleaning solution. This method is also very environmentally friendly.
It can be seen from the above three methods that the latter two methods have low impact on the environment, and the third cleaning method has high investment cost and complicated process. Therefore, each printing plant should choose the appropriate anilox cleaning method in combination with the actual situation of the factory.
Recovery cycle system
The recycling system for storage containers and cleaning cloths (for recycling and reuse) has been widely established in many countries.
Recycling means the reuse and processing of a product or part of it in a circulatory system. The circulatory system produces secondary raw materials and saves resources and waste by this means, thereby reducing the degree of pollution to the environment.
Through the above analysis, it is possible to effectively control several major factors affecting the environment and safety in flexographic printing. Of course, these control methods are not uniform. In the actual production process, each printing factory should select the appropriate environmental and safety improvement methods based on the actual situation of its own factory.