Analysis of Screen Printing and Environmental Protection (I)

Abstract Environmental protection is a basic national policy of our country. The exhaust gas emitted during screen printing production has a certain influence on the air quality of the local environment. The status quo of environmental protection in printed circuit manufacturing industry, the type of exhaust gas emitted from it, its treatment methods, waste reduction measures and some technical problems to be solved urgently are described. At the same time pointed out the way out of environmental protection - must adopt clean production technology.

Keywords environmental pollution waste gas

1. introduction

In the 1950s and 1960s, due to the rapid growth of handicrafts, the pollution of human emissions exceeded the earth's capacity and self-purification capacity, resulting in global environmental pollution and triggered a series of public hazards that endanger human life, health and safety, such as smoke. , acid rain, water crisis, greenhouse effect, ozone layer destruction, etc.

The global environment deteriorated further in the 1980s and threatened the sustainable development of the economy. How to coordinate the environment and sustainable development is a problem that needs to be solved urgently in the world. People's understanding of the environmental pollution caused by industrial wastewater discharge is relatively straightforward and profound, and early formulation of industrial wastewater discharge standards; while the understanding of volatile solvents causing damage to the atmosphere is lagging behind, it has only recently become apparent that they have become volatile. The severity of the damage caused by solvents to the atmosphere. In 1990, the U.S. Department of Environmental Protection established the “Air Clean Act” to limit the use of volatile organic compounds. California, USA, stipulates and limits the use of volatile organic solvents. The European Community has also enacted legislation to allow the content of solvent exhaust gases to be allowed to evaporate into the atmosphere. It can be foreseen that in the near future, following the United States and the economically developed countries, the environmental protection departments of other governments will also successively put forward measures to deal with environmental pollution and limit their use.

Environmental protection is a basic national policy of our country. In recent years, China has attached great importance to the management of environmental protection and environmental pollution, and has issued many environmental protection laws and regulations. Such as this year, Xiu Ting’s Law on Prevention and Control of Atmospheric Pollution, various large and medium-sized cities have successively carried out reports on the ambient air quality in the urban areas. Although the air pollution around the environment in the screen printing industry is not as serious as those in the automobile, chemical, and electroplating industries, the air pollution caused by the local environment cannot be ignored. The air pollution and environmental protection issues in the screen printing industry must be aroused. We attach great importance to it.

2. Industry environmental protection

Screen printing in the electronic information industry is mainly used in printed circuits, membrane switches, sign manufacturing, thick film circuits, plastic parts screen printing and other industries. With the vigorous development of the information industry in recent years, the ancient screen printing process has been widely used in the information industry products, such as the printed circuit manufacturing industry. Many foreign, Hong Kong-funded and Taiwanese-funded enterprises transferred printed circuit products to the SAR and the Mainland for processing and manufacturing, and investing and setting up factories in the mainland directly promoted the rapid development of the printed circuit industry. Its production scale and production volume have been increasing year by year, and the proportion of its output value in the electronics industry has also been increasing. However, environmental pollution is also increasing. For some large companies, the integrated treatment of waste water and waste gas has been taken into account through the comprehensive environmental assessment during the construction of the plant. For many small and medium-sized enterprises, environmental protection has not yet been mentioned on the agenda. The decision-making and management of enterprises have not seriously considered the issues of environmental protection, waste water and waste gas treatment, or they have encountered difficulty in capital, technology, site, and governance. There are no concrete reasons for such reasons. In particular, in areas where the screen printing industry is relatively concentrated, some small and medium-sized factories or home-plants have a relatively weak environmental awareness. In terms of environmental protection, there are few or no resource allocations such as technology, personnel, equipment, and funds. Investing in exchange for economic development at the expense of the environment is a repeat of the mistaken path that the industrialized country has adopted in its early days.

For the printed circuit manufacturing industry, wastewater treatment is generally considered more important, and the treatment of exhaust gas is relatively lacking. Therefore, the screen printing industry should treat exhaust gas treatment as a research topic to effectively solve it.

3. Air pollution sources in the printed circuit industry

In the printed circuit manufacturing industry, the emission of exhaust gas can be divided into three types according to the characteristics of its production process and the characteristics of air pollution produced by pollution sources:
Volatile organic waste gas;
Acid, alkaline chemical waste gas;
Dust exhaust.

The exhaust gas emitted by the printed circuit industry is characterized by a large number of exhaust gases. The components are more complex and less concentrated. Some organic exhaust gas and acid-alkali waste gas are mixed and discharged, resulting in unbalanced emissions and difficult handling.

3.1 Volatile Organic Waste Gas

The printed circuit board industry uses a lot of ink printing materials containing high molecular compounds, such as thermosetting printing materials, liquid photosensitive printing materials, and light curing printing materials. Ink printing materials mostly contain solvents, which are added in order to obtain suitable printability. The diluent, the solid content of the ink printing material is usually between 65% to 85%, the solvent or diluent content is 15% to 35%. The solvent or diluent is composed of several components of organic compounds (VOC, Volatile Oraganic Compounds) such as alcohols, ketones, benzenes, and ethers. The solvents and diluents composed of VOCs easily evaporate and evaporate at room temperature and during heating, and form ozone layers in the air. This ozone layer is different from the same-temperature ozone layer that protects the Earth from UV rays. It is a VOC in a low-flow layer. It produces photochemical smog under the effect of photochemistry. This smoke mixed in the air affects people’s eyes, skin, and The oral respiratory tract and its health have an adverse effect.

Volatile organic compound exhaust gas mainly comes from the circuit, solder mask, text ink printing operation, hot air leveling process and solvent materials stored in the warehouse. The normal treatment method for the operation process is to use the suction-type gas collection system to collect the waste gas, but the convenience of the production process and production unit operation, and at the same time, due to the excessive air suction, the solvent volatilization is accelerated or aggravated, resulting in difficult air flow. The control causes the screen printing ink to dry too fast, resulting in a blocking phenomenon. However, due to the high height of the gas hood, the gas gathering effect is generally not good. In addition, most of the plant enterprises use the filling or scrubbing tower to clean the water for the volatile organic waste gas, or treat the tower with acidic and alkaline chemical waste gas. Merge and handle together. Since the organic compounds contained in the organic waste gas are hydrophobic substances, a wet treatment method is used, and the removal effect thereof is quite limited, and only the exhaust gas in the indoor work place is collected and discharged into the atmosphere. Therefore, the dry treatment must be used, and the activated carbon adsorption or incineration treatment may be more effective and reliable.

In the warehouse, most inks, solvents, and thinners are usually stored, which often results in high indoor air content. At the same time, some solid materials also contain organic exhaust gas. Usually, a direct-row ventilation fan is used to suck the exhaust gas in the warehouse. It is discharged into the outdoor atmosphere without any treatment. Similarly, some thermosetting printing materials are dried and cured in a forced air circulating oven, and are not processed during drying. Usually, they are discharged directly to the outside using a direct-discharge type pipeline, and the local air quality causes adverse effects.

(to be continued)