Environment and safety in flexographic printing

This paper makes a detailed analysis of the main processes and materials used in flexographic printing in terms of printing environment and safety, and puts forward specific methods for controlling environmental pollution factors and improving the printing plant environment.

Green environmental protection has become the theme of development in the new century. The problem of greening in modern printing has become a major problem that hinders the sustainable development of the printing industry. Initiating green projects, developing green products, and adapting to environmental protection requirements have become urgent tasks. 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.

The original name of flexographic printing was "flexographic printing." It was named after the printing of volatile inks made with flexographic dyes. Because flexographic printing is toxic, its printing range is greatly restricted. With the continuous development of powder flexographic printing technology and the increasing range of applications and the promotion of non-toxic, residual latent agents, environmental pollution-free water-based inks, Uv oil and drunk soluble oil, it has been adapted to environmental protection and green packaging. The requirements have therefore grown rapidly. Although flexographic printing greatly reduces the pollution to the environment compared to other printing methods, it is only relative to the flexographic process, no matter how advanced technologies, processes and materials are used Is complete and pollution-free. Therefore, in order to achieve further greening of flexographic printing, in addition to pursuing perfection in materials and processes, flexo operators and managers need to make greater efforts in practice to reduce environmental pollution. The following will discuss several important factors that affect the environment in flexographic printing.

Environmental factors in the process of plate making

1. Development process

An important aspect that affects the environment during the plate making process is the application of the developer. Flexible plate material has gone through the development process from rubber plate to photosensitive resin plate. Due to the excellent characteristics of photosensitive resin plate, it has been widely used. The flexographic processing is done in a dedicated processing machine. The developing solution mostly uses a hydrocarbon-based solvent (trinitroethylene) as the main solvent. However, trichloroethylene is toxic and its volatility is very strong. Note that the tertiary ethylene vapor in the air cannot exceed the poisoning limit. In addition, three atmospheres of ethylene will decompose when light, air, and moisture coexist to produce harmful hydrogenated hydrogen acid gas, causing metal corrosion. Therefore, in the process of use, there must be special cleaning equipment, which can recover the developer for recycling and is preferably in a closed form. A better way is to develop a solvent with less side effects to replace tertiary ethylene.

2. Debonding process

Debonding is to de-drill the layout with light or chemical methods. The purpose is to remove the drilling on the surface of the plate and enhance the powder capacity.

â‘ Chemical method

The method is to immerse the dried printing plate in a well-drilled solution in the dish for chemical treatment. There are two types of chemical de-grading (aqueous bleach solution) and austenite (hydrochloric acid and austenite solution). The solution is extremely tolerant to the environment, so this method has gradually become unacceptable to people during the process of de-drilling.

â‘¡Lighting method

This is a commonly used method, which is accomplished by irradiating the Australian solution coffin with ultraviolet c (UV-c light source). Compared with the first method, the environmental pollution caused by the light method is much lighter, but it should be noted that this solution after short-wave radiation in the light method is also harmful to the environment, and the waste liquid should be properly treated.

In LabeExpo in Chicago in September 2000, DuPont launched the Cyrel Express System. This is a completely digital dry platemaking system. The essence is a hot processed version, the entire processing process is in a completely dry state.

Since no solvent is needed, it completely avoids the environmental pollution problem caused by the solvent. In addition, it greatly reduces the plate-making time, and the processing process becomes faster without drying.

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Environmental factors in ink applications

At present, the oil is the biggest source of pollution in the printing industry. The world's oil production has reached 3 million tons per year. The annual global VOc (organic volatile) pollution emissions caused by inks have reached hundreds of thousands of tons. These organic volatiles can form a more serious greenhouse effect than cO2, and the formation of oxides and photochemical smog under the sunlight will seriously pollute the atmospheric environment, which has attracted wide attention from all sides. Among various printing methods, only flexographic printing has generally adopted environmentally friendly green printing materials-water-based ink, Uv ink and drunk ink. Here we mainly introduce the first two.

1. Water-based ink

The biggest feature of water-based ink is that it significantly reduces the emission of voc (organic volatiles), thereby preventing atmospheric pollution and improving the printing environment, which is beneficial to the health of workers. It can completely eliminate some toxic and harmful substances in the solvent-based inks to the human body and the pollution of packaging products, improve the overall environmental quality f is particularly suitable for food, beverages, pharmaceuticals and other strict sanitary packaging and printing products. In addition, it can not only reduce the fire hazard and concealment caused by static electricity and flammable solvents, but also reduce the residual solvent odor on the surface of the printed matter.

As people's call for environmental protection is getting higher and higher, the status of water-based ink will be more and more important, and its use will inevitably be more extensive. Therefore, we must control the characteristics of water-based inks more strictly to minimize the pollution to the environment. Although the water-based ink obviously reduces the VOc row placement, we hope to control this emission f to a lower level. In the air cleaning program implemented in California a few years ago, the requirement for organic volatiles in water-based inks to not exceed 3%. In addition, many users and manufacturers also have restrictions and requirements on the content of heavy metals in water-based inks. This means that in the formulation of water-based inks, pigments should be properly selected to exclude pigments with high levels of heavy metal ions.

2.Uv ink

Uv radiation curing products (including Uv inks and Uv varnishes) are known as "new green industrial technologies for the 21st century" for their high efficiency, energy saving, no solvent emissions, no environmental pollution, and excellent product performance. The US Environmental Protection Agency agrees. In the past 10 years, the application of UV oil and UV varnish has become increasingly popular. According to statistics, the US used flexo printing UV inks in 2001 to reach 3500 tons.

UV ink is not only a solvent-free safety oil, but also has many excellent characteristics. For example, it is not easy to paste, the dots are clear, the ink color is bright and bright, the chemical resistance is excellent, and the amount of consumption is saved. The promotion and application of UV oil not only benefits the environment but also improves the quality of flexo products, and promotes the further development of flexo technology.

In terms of environmental protection, UV ink is indeed a very ideal ink. It should be noted that most UV products can be regarded as skin irritants before drying. However, due to the low volatility of these products, if you can maintain the habit of wearing skin care gloves and eye protection during operation, you will reduce such problems. In addition, it is necessary to provide follow-up treatment of the exhaust system because the old UV ink will emit oxygen.

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Environmental impact during cleaning of anilox rolls

In flexographic printing, the anilox roller is an extremely important unit in the process of ink transfer. Its surface is covered with particularly fine meshes. Through these meshes, the ink transfer is achieved, and the ink clogged meshes are flexographic. Very headache in printing. Usually the mesh clogging is caused by the anilox roller being clogged by the dry oil button during the working process. Therefore, the anilox roller should be cleaned in a timely manner during the printing process.

The cleaning methods are generally as follows:

1. Strong corrosion chemical cleaning method

Evenly apply the corrosive cleaning agent (usually an alkaline solution) on the surface of the anilox roller. If necessary, wrap a layer of plastic products on the surface of the anilox roller to prevent the chemical solution from volatilizing. The anilox roller is ablated for 1-48 hours. After the ink is sufficiently softened, the anilox roller is cleaned with water or alcohol solution (acid solution such as acetic acid is not available) combined with manual cleaning method. This type of cleaning method has a good cleaning effect, but it has a certain corrosive effect on the anilox roller and will cause environmental pollution.

2. Jet cleaning method

Spray the baking soda softening cleaning medium to the surface of the anilox roller to crush the solidified ink to achieve the purpose of cleaning. Baking soda is easy to dissolve and non-toxic. Its crystal body is easy to break when it touches other substances, and it will not damage the surface of the anilox roller and the ink cavity wall. Therefore, this cleaning method has a good cleaning effect, and has a promotion and use price.

3. Ultrasonic wave washing method

Immerse the mesh roller in an ultrasonic cleaning tank filled with a chemical cleaning solution. During cleaning, the anilox roller rotates slowly. The frequency conversion device that can send high-frequency sound waves in the tank starts to work to make the solution vibrate and generate bubbles, causing an inward explosion The explosive force expels the ink from the net hole and flows away with the cleaning liquid. This method is also very environmentally friendly.

It can be seen from the above three methods that the latter two methods have low environmental impact, while the third cleaning method has high investment cost and complicated process. Therefore, each printing factory should choose the appropriate anilox cleaning method based on the actual situation of the factory.

Recycling system

Storage container and cleaning cloth recycling systems (for recycling) have been widely established in many countries.

The meaning of recycling is: the reuse and disposal of products or part of them in a recycling system. The recycling system produces secondary raw materials and saves resources and waste through this approach, thereby reducing the degree of pollution to the environment.

Through the above analysis, several major factors influencing the environment and safety in flexographic printing can be effectively controlled. Of course, these control methods are not the same. In the actual production process, each printing factory should combine the actual conditions of its own factory to choose the appropriate environment and safety improvement methods.

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