Application of the hottest corona treatment in BOP

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Application of corona treatment in BOPP film processing

the surface tension value of polypropylene material itself is only 31 dynes, and the film surface tension is generally required to be above 38 dynes

there are two common surface treatment methods: one is corona treatment; The other is flame treatment. Principle of corona treatment: the film passes between two electrodes with high voltage. The high voltage ionizes the air between the electrodes, generates electron flow, and forms an oxidative polarization group on the surface of the film, making the surface of the film polar, which is convenient for the adsorption of printing ink

flame treatment is to use a specific blowtorch to burn gas and air with a certain composition and proportion to form an oxidation flame with a temperature of 2100~2800 ℃ to achieve the purpose of instantly changing the surface properties of the film. In the actual treatment process, the temperature of the flame, the distance between the flame and the film and the treatment time are important factors affecting the treatment effect

corona treatment is simple and effective, so BOPP manufacturers basically adopt this method. The following is a discussion on the test and control of corona treatment in BOPP processing and its influence on the film properties

1.1 determination of corona treatment intensity of BOPP film

the test method commonly used for the surface tension of BOPP film is the coating method. Its principle is to mix formamide and ethylene glycol ether in different proportions to obtain a series of test solutions with different factorial values. During operation, smear the test solution on the surface of the film, and the corresponding dyne value of the test solution whose liquid level breaks in 2 seconds indicates the corona treatment intensity of the film

2. Factors affecting the intensity of corona treatment of BOPP film

the corona processor is composed of electrodes, high potentiometers and silicone rubber rollers. When the voltage passes through the 2.5mm air gap, continuous discharge will occur. In addition, in order to eliminate the generated ozone and reduce the temperature, exhaust the air near the corona processor with an exhaust fan 16 Machine weight: About 180kg, and use process water cooling inside the silicone rubber roller to dissipate heat. The main factors affecting the effect of corona treatment are as follows:

2.1 electrode type

the effect of corona treatment is closely related to the design of electrode. There is a certain difference in the treatment effect of using single electrode or double electrode on the equipment. Compared with single electrode, double electrode has several advantages: 1. It can produce higher treatment value and lower energy consumption; 2. It can reduce the decrease of surface tension during storage; 3. Reduce the heating of the film during corona treatment; 4. Reduce surface induced static electricity

2.2 film temperature

bopp is a film made by extruding thick sheets after chilling, and then stretching in both vertical and horizontal directions. After entering the traction unit, it goes through the processes of cooling, trimming, thickness measurement, preheating, and then corona treatment. At this time, the temperature of the film has a direct impact on the effect of corona treatment, and the film temperature is mainly controlled by the set temperature of the preheating roller.

with the increase of the film temperature, the dyne value of the surface treatment of the film also increases. Adjusting the film surface treatment dyne value through the set temperature of the preheating roller is one of the effective methods often used in process control

2.3 production line speed

production line speed is another important factor affecting the effect of corona treatment. BOPP film passes through the high-voltage electrode gap in a very short time, so that the surface dyne value can be improved. The length of residence time in the high-voltage electrode gap will affect the corona treatment effect of the film

it can be seen that the electrode voltage of corona treatment should be adjusted accordingly with the change of production line speed, and increase with the increase of production line speed

2.4 electrode exhaust volume

in the corona treatment process, with the ionization of air, plasma will be produced, including electrons, oxygen ions, ozone, etc. the plasma will penetrate the film, destroy other chemical bonds, excite free radicals, and act with oxygen ions to form oxidative polarization groups, which will affect the surface wetting characteristics of the film. On the other hand, the concentration of plasma on the film surface will directly affect the effect of corona treatment. Generally speaking, the larger the opening of the electrode exhaust valve, the smaller the dyne value of the film surface treatment; On the contrary, the smaller the opening of the electrode exhaust valve, the greater the dyne value of the film surface treatment

2.5 surface materials

bopp production will involve different materials and added masterbatches. BOPP can be divided into heat sealed type and non heat sealed type. The basic materials on the surface layer are copolymer and homopolymer respectively. Due to the differences between the two materials, there is a certain difference in surface tension between the two after undergoing the same corona treatment. Generally speaking, for copolymers, such as Solvay ks413, Montel plz679, basic ep5c37, etc., which are commonly used at home and abroad, the surface efficiency of the ionomer penetrating into the film is greater than that of homopolymer, Therefore, the heat sealed film will be easier to achieve higher processing strength

in addition, in the formulation design of heat sealing films, in order to meet the requirements of packaging machines, it is usually necessary to use a lubricant to improve the friction performance with the lowest heat transfer coefficient of the film. When choosing a lubricant, silicone lubricant should be avoided as much as possible. This is because the surface tension of silicone is relatively low, which is about 12 dyne at room temperature, which is a big gap with 31 dyne of PP, The surface tension value of BOPP will be greatly reduced by using silicone smoothing agents

antistatic agent will also have a certain impact on the corona treatment effect of BOPP film. Most of the antistatic agents are added to the core layer, which has mobility. The antistatic agents penetrating into the surface will affect the surface corona treatment characteristics of the film, and the treatment intensity will be reduced to a certain extent

2.6 surface material

bopp film will also change its structural state after production. Within a few days, the polymer will change from amorphous to crystalline, thus affecting the effect of corona treatment. The treatment intensity will gradually decrease with the passage of time, and finally remain stable. The reduction range of corona treatment is related to the storage temperature. The higher the temperature is, the faster the reduction range is

3. The effect of corona treatment on the physical properties of the film

corona treatment can not only change the surface dyne value of the film, but also affect other physical properties of the film, mainly including the following aspects:

3.1 friction coefficient

because the principle of corona treatment is that the film passes through two high-voltage electrodes to produce electron flow, making the film surface produce polarity, and compared with the non film treatment surface, Additives (including antistatic agents and smoothing agents) located in the core layer of the film are easier to exude through the film treatment surface. Taking the ABA type film, that is, the film with the same formula structure on the inner and outer surfaces, as an example, the friction coefficient of the inner and outer surfaces of the film without corona treatment is the same, but after corona treatment, the friction coefficient value of the film treated surface is lower than that of the non treated surface

from production to 14 days later, the additives in the film core are in a high-speed migration period, and the static and dynamic friction coefficients of the treated and non treated surfaces show a rapid downward trend, and the value tends to be stable after 14 days. On the whole, the friction coefficient of the treated surface is lower than that of the non treated surface

3.2 shrinkage rate

the shrinkage rate of the film will decrease to a certain extent due to certain heat generated during corona treatment

3.3 heat sealing strength

when producing BOPP heat sealing film, the material used for the surface layer is ethylene propylene copolymer. As mentioned above, copolymers only need relatively low treatment voltage to achieve the same treatment strength in actual production. However, it should be noted that too high corona treatment value will lead to the universal mechanical experimental machine for college teaching between copolymers. The main technical index: crosslinking, resulting in the loss of heat sealing efficiency of heat sealing film. Therefore, in the actual production of heat sealed films, especially when adjusting the higher corona treatment value, the heat sealing strength is a necessary detection measure

4 conclusion

(1) when corona treatment is applied to the production of BOPP film, the liquid coating method is basically used in the test

(2) the factors that affect the effect of corona treatment mainly include electrode type, film temperature, production line speed, electrode exhaust volume, and surface material

(3) corona treatment will affect the physical properties of the film, such as friction coefficient, shrinkage and heat sealing strength

influence of temperature on BOPP production

in the production process of BOPP, temperature is a very important production process parameter. It is expected that domestic mines will still be weak in the near future. Good temperature control is the basic guarantee for producing high-quality films. The temperature control of each processing section in the production process has its different ways and characteristics. From the control of cold roll temperature, longitudinal and transverse stretching temperature,

source: Network

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