How to eliminate the influence of static electricity in photovoltaic glass packaging on the peeling of backing paper
Photovoltaic glass is large and easy to break, so it should be well protected during transportation. As a kind of spacer between glass and glass, the mould proof lining paper can not only prevent glass from being scratched during transportation, but also extend the storage time of glass. The lining paper supplier shall cut different sizes according to the specifications of glass in advance. During the packaging process, the lining paper and glass shall be put into the packaging box by hand alternately. With the vigorous promotion of "Industry 4.0 helps to achieve Made in China 2025", it is a general trend to replace labor with stable machinery and equipment. However, while paper laying by machines brings convenience, static charges will be brought into the packaging due to friction between the paper liners and the technological characteristics of the equipment during the working process of the paper spreader. During the use of component enterprises, the paper liner and glass cannot be separated quickly. See Figure 1. Additional manual pulling is required, The production efficiency will be affected, and production will be stopped in serious cases. The customer complains strongly. It is urgent to solve this problem quickly.
Fig. 1 Unable to separate glass and backing paper due to static electricity
1 Structure and performance analysis of paper spreader
1.1 Basic structure and working process of paper spreader
The paper spreader can be divided into three parts:
Web lining paper - lining paper to be laid, in the form of web paper, placed in the paper spreader; There are certain requirements for the quantity (weight per square meter, also known as gram weight, unit: g/m2), pH value and moisture content of lining paper;
Mechanical part - several groups of roll shafts that can be adjusted. By adjusting the height of the roll shaft, the length of the cutting lining paper can be controlled to ensure that the lining paper can be spread evenly on the glass surface;
Electrical part - the control mechanism of the paper spreader, which controls the speed of the mechanical device and the application amount of the electrostatic rod according to the size of the lining paper cut.
Working process: according to the glass size, select the standard web paper and load it into the paper spreader; Input the specification information and customer requirements into the equipment, start the equipment, adjust the applied electrostatic amount, debug the size of the first piece, check the lining paper laying quality, confirm the normal production after completion, and inspect the lining paper laying quality and web paper allowance every hour.
1.2 Advantages and disadvantages of paper spreader
The characteristics of paper spreading machine and manual paper spreading are shown in Table 1.
Table 1 Comparison between paper spreading machine and manual paper spreading
It can be seen that the paper spreader has obvious advantages, and it is the general trend to use and promote the paper spreader to replace manual work.
2 Source and distribution of static electricity in packaging
2.1 Main sources of static electricity
In the glass packaging process, the static electricity of lining paper mainly comes from internal generation and external introduction.
(1) Static charge generated inside: when two or several kinds of solid materials with different properties rub or contact with each other in a large area, the electrons between objects are transferred. During the lining paper laying process, the friction between the paper rotating with the web, the friction between the lining paper and the drive roller shaft of the paper spreader, the friction between the glass and rubber transmission roller table, and the friction between the operator's chemical fiber, wool clothing and the glass/lining paper during the product packaging/unpacking process can all produce static charges.
(2) External introduction of static charge: the process characteristics of the paper spreader, applying static electricity to ensure that the paper is stretched and tiled.
2.2 Principle of static electricity storage of lining paper
When two objects of different materials are in close contact, a double electric layer is formed on the contact section. For example, both objects are conductors. When two objects are separated, although the separation speed is very fast, electrons can always easily pass through the separated contact point and all leak back to the original place. Therefore, they still behave as electrical neutrality after separation; If two or one of the materials is an insulator material, there will be extra electrons or remain on the object after separation, which shows the electrification. The resistivity of the backing paper is above 108 W · cm, with high resistivity and poor conductivity. When it gets electrons, it is difficult for electrons to move on it, so static electricity is easier to accumulate.
2.3 Distribution of static electricity in glass package
With the common 3.2 mm × 1644 mm × Take the packaging of 130 pieces with 986 mm specification as an example. The charge distribution at different positions in the overall packaging is shown in Figure 2.
Fig. 2 Distribution of electrostatic quantity in packaging
Note: The data from bottom to top indicate the electric value of the top five pieces of the packing box, the middle five pieces of the packing box, and the bottom five pieces of the packing box.
From the distribution of static electricity in the package, we can get:
(1) The charge carried by photovoltaic glass and lining paper is negative;
(2) The charge distribution is from top to bottom, and the electrostatic value shows a downward trend. The electrostatic charge on the top of the packing box accumulates more;
(3) Under the same production conditions, there are differences in the amount of charge between different packaging boxes for the same product.
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