Now plastic flexible packaging has been widely used in various fields of commodity packaging. The most commonly used non-polar films such as polyethylene and polypropylene for flexible packaging are non-polar materials. The surface is dense and smooth. It is an inert surface with a surface free energy of only 2.9 ～ 3.0 × 10ˉ6J / cm2. Theoretically, a film with a surface free energy lower than 3.3 × 10ˉ6J / cm2 cannot infiltrate any of the currently used adhesives. Therefore, it is necessary to pass the surface treatment to make the surface free energy of the film reach 3.8 ～ 4.0 × 10ˉ6J / cm2, which is beneficial to obtain good composite strength. There are many commonly used thin film surface treatment methods, among which corona treatment is a commonly used method.
The three gravure printing machines used in our factory are equipped with corresponding corona treatment equipment. When processing is needed, the film can be inserted between the electrode rollers in order. The processed film directly enters the printing unit, and the adhesion of ink on the film is good. The installation of corona treatment equipment on the dry laminating machine is one aspect of our factory's technical transformation. The purpose is to increase the surface tension of the polyethylene hydrocarbon film and improve the adhesion fastness of the composite product. After the plant equipped with the corresponding spark treatment equipment on the dry compound machine according to the actual situation, it has achieved very good results. The treatment equipment adopts DCD16-2-10 plastic surface treatment machine produced by Dalian Radio No. 9 Factory. After corona treatment, the surface tension of the film can reach 3.8 ~ 10ˉ 2N / cm2, which greatly improves the peel strength of the composite film and can fully meet the quality requirements. It is of great help to the aluminum coating, especially the BOPP aluminum coating, but it must be changed in the installation and wiring of the equipment. The following will discuss the corona treatment principle, surface tension detection method, equipment installation wiring and common troubleshooting.
1 Corona treatment principle
Electric shock or breakdown, under the action of high voltage electric field, the strong impact of the electron flow on the plastic film can make the film surface fluff, become rough, and increase the surface area. When the adhesive is in contact with its surface, it can produce good wetting, the adhesive will penetrate into the grooves that have been brushed, and the film will be firmly bonded by the "anchoring" effect. This is a physical effect. Compared with the untreated film, the film after it is obviously uneven and rough, and the electric shock strength can be enhanced with the increase of voltage and current.
2 Increase the polarity of the film
Under the action of a high-voltage electric field, the oxygen in the air becomes ozone, and ozone is decomposed into oxygen and new ecological oxygen atoms. The new ecological oxygen atom is a kind of strengthening agent, which can oxidize the a-carbon atom in the polyethylene or polypropylene molecules to form carbonyl and hydroxyl groups. With this structure, the film's molecular integrity increases and the surface tension increases. The affinity of the adhesive increases, and the adhesion fastness between the composite films increases. In addition, due to the generation of hydroxyl groups, new a-carbon atoms in the molecular chain will appear active hydrogen. This active hydrogen can react with the active group isocyanate (-NCO) in the polyester adhesive to cause the A strong chemical bond is formed between the adhesive material and the adhesive, which increases the adhesion fastness. From the infrared light detection, it was found that there was a carbonyl absorption peak on the surface of the treated polyolefin film on the line, proving the existence of the above chemical action.
3. Commonly used detection methods
1. Use BOPP single-sided transparent adhesive tape for peeling inspection, stick the BOPP single-sided tape on the surface of the film to be tested, compress it and then tear it. If the surface tension of the film meets the requirements for use, the peeling is very hard and the sound is low; on the contrary, it is easy to peel and mix with a rustling sound.
2. Test with Dyne pen: When the surface tension value of the film meets the requirements, BOPP: 3.8 × 10ˉ2N / m; PET: 5.0 × 10ˉ2N / m; nylon: 5.2 × 10ˉ2N / m. The liquid marks on the place where the test pen strokes are even, without shrinking. If a part shrinks and a part does not shrink, it means that the treatment is not enough. It is worth mentioning that when testing PET and nylon, a large-level test pen must be used. The common specifications of the surface tension test pen are: 3.8 × 10ˉ 2N / m; 4.0 × 10ˉ 2N / m; 4.2 × 10ˉ 2N / M; 4.4 × 10ˉ2N / m; 4.8 × 10ˉ2N / m5 types (for measuring aluminum foil).
3. Prepare the surface tension test solution as shown in Table 1:
The treated film should not be left for too long, at most 7 days, the longer the time, the more obvious the surface tension value decreases. If it needs to be left for a long time, the initial value of surface tension should be increased when processing the film.
4. Common equipment faults and troubleshooting methods
SDCD16-Z-10 corona treatment equipment sometimes has some failures during use, including electrical failures and mechanical failures. The following is a classification analysis of the problems I encountered in actual work for reference.
1. The device does not generate sparks, impact the positive electricity on the rack and the aluminum row does not discharge. This kind of failure often occurs in the rainy season. Due to the high indoor humidity, there is water on the discharge aluminum row on the impact rack and the insulator silicone rubber roller, which causes the positive electrode to discharge and the aluminum row cannot be discharged. The treatment method is: turn off the total power supply, and dry all the rollers (including the traction roller and the insulating silicone rubber roller) and the discharge aluminum row of the impact rack with a dry cloth. And the electric blower is used for heat treatment. If there is no water, the discharge equipment can work normally. After encountering the above situation, the impact machine should be opened from small to large. Observe the spark status at the same time. The normal spark is continuous, without red dots, and even.
2. The discharge aluminum row does not discharge, the voltage does not rise (referring to the KV meter), and the current (A) indicates that it is too large. Reasons: The processing equipment is connected in parallel, the diode is damaged, or the series is damaged, the capacitor is damaged; the wiring of the high voltage transformer is wrong; the SCR in the processing equipment is damaged and broken; the carbon brush of the high voltage transformer is not in good contact or there is oil on the slip ring; the control panel The overcurrent switch on the circuit board is damaged; the triode on the circuit board is damaged and cannot be amplified; the winding of the high-voltage transformer is broken or the insulated porcelain bottle is damaged; the positive and negative electrodes of the output terminal of the high-voltage transformer are connected, and leakage or breakdown occurs. Countermeasures: measure the capacitance and resistance of the diode, and replace it if damaged; correct wiring, green wire in the middle, red wire on both sides; replace the thyristor tube; check the carbon brush, and grind with 1000 # water-resistant sandpaper, Until clean; replace the overcurrent switch; replace the triode; carefully check the winding, replace the insulating porcelain bottle; replace the wiring of the same model and the same specification; replace the new AC contactor.
3. When processing BOPP and PE films, the discharge aluminum discharges electricity, while when processing VOPPP and VMCPPP films, the discharge aluminum row does not discharge. Reason: The diode of the processing equipment was broken; the silicon rubber insulating roller on the impact frame was broken. When processing VOPPP, a "snapping" sound was heard, and the spark was only a little; the positive and negative wires of the output terminal of the high-voltage transformer touched Conductor, even leakage or breakdown; wrong connection of positive and negative electrodes; oily or too dirty on discharge aluminum row. Countermeasures: replace the diode; replace the silicone rubber insulating roller; the connecting wire should be suspended in the air, and can not touch the conductor, if it breaks down, it should be replaced; replace the positive and negative wiring; wipe the oil and other clean.
During the use of SDCD 16-2-10 corona treatment equipment, the discharge aluminum row can be adjusted according to the width of the material, but it is strictly prohibited to touch it by hand to ensure safety. After testing the treated film, the surface tension value is sufficient, not the bigger the better, it is worth mentioning: when impacting VOPPP, VMCPPP film, the high and low transformers must be swapped with the positive and negative wiring on the impact frame, that is, That is to say, the positive pole on the impact rack is connected to the negative pole, and the negative pole is connected to the positive pole or live wire.
The application of the spark point treatment equipment in the dry compound machine greatly improves the product compound strength and quality. In the actual use and installation process, it must be operated by professionals and pay attention to the safety of use.
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