JPS628448B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for improving the corona discharge treatment effect to a degree that is sufficiently satisfactory at the actual production level. Electric discharge treatment of plastic molded products is a technology that has been used for a long time, and is indispensable for surface modification of plastic films (including sheets, hereinafter the same), such as polyethylene films and polypropylene films. . The various plastic molded products described below are also considered to be a useful means for improving quality, and the range of benefits and applications is expected to expand in the future. However, for this purpose, it is necessary to improve the processing efficiency itself by corona discharge treatment and explore its possibilities.Although extensive improvement research has been carried out so far, it cannot be said to be sufficient. For example, Japanese Patent Publication No. 48-17747 describes a technique for promoting chemical changes on the discharge surface by supplying an organic solvent to the discharge section, but residual solvent in the plastic molding is a problem. It doesn't suit the current situation. Mata JOURNAL OF
APPLIED POLYMER SCIENCE Vol 15PP1365
1375 (1971), it is described that corona discharge treatment is performed in an inert gas atmosphere, and it is suggested that the influence of activation or deterioration on the surface of plastic molded products may occur. Techniques for performing corona discharge treatment have also been proposed, but conventional methods, such as the method disclosed in Japanese Patent Publication No. 56-18381, require a large amount of inert gas, resulting in high costs. In addition, the method of JP-A No. 57-23634 (corona discharge technology under an inert atmosphere for a running film) requires a special shield structure to block the atmosphere that is entrained by the film, making it difficult to use the device. Although the surroundings become complicated, the amount of inert gas fed is unnecessarily large, and a complete or almost complete inert atmosphere is not formed, so a low treatment level has to be satisfied. For this reason, taking film as an example, it has the disadvantage that high-speed processing is not possible, resulting in a significant drop in productivity.On the other hand, if you try to increase the processing effect by using low-speed processing, the appearance of the film due to surface damage. Defects such as defects and increased blocking occur, and it can only be said to be completely unsatisfactory at the level of actual production. The present invention has been made with attention to this situation, and is the result of intensive research aimed at developing a technology that does not require special and large-scale equipment and does not require the consumption of large amounts of gas for shielding. The result is complete. However, the corona discharge treatment method according to the present invention is a corona discharge treatment apparatus in which at least one pair of electrodes are arranged facing each other, and the discharge side electrode is surrounded by a hood, in which plastic molded articles are continuously carried in. When performing corona discharge treatment, a gas other than air or oxygen is introduced into the hood, and the gas is actively discharged from the side or bottom of the discharge side electrode to the outside of the hood while corona discharge is performed. The gist of this is that it performs processing. Plastic molded articles to which the method of the present invention is applied include, in addition to the above-mentioned films and sheets, long articles such as fibers, pipes, tapes, woven fabrics, and nonwoven fabrics. If the present invention is applied to corona discharge treatment by transporting the molded product in the longitudinal direction and passing it through, the effect will be dramatically exhibited, but even with other molded products, the process can be carried out at a constant speed. As long as the corona discharge treatment is applied while the process is being carried out, great technical effects can be obtained by applying the present invention. Polymers constituting the molded product include polyamide, linear polyester, polyolefin,
Thermoplastic resins such as polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polystyrene, and polyvinyl alcohol; thermosetting resins such as phenolic resin, urea resin, melamine resin, unsaturated polyester resin, and furan resin are used. In addition, molded products made using these resins contain stabilizers, lubricants, anti-blocking agents, antifogging agents, ultraviolet absorbers, flame retardants, clarifying agents, antioxidants, light stabilizers, antistatic agents, and dyes. All materials that may contain additives such as pigments and do not adversely affect the implementation of corona discharge are included as objects of the present invention, whether alone or in combination. The configuration and effects of the present invention will be clarified below based on the drawings of the embodiments, but the structure and arrangement of the discharge side electrodes, the shape of the hood, etc. shown in the drawings are only representative examples. Since only an example of application to plastic film is shown, it is within the technical scope of the present invention to change the design on the condition that it does not go against the spirit of these descriptions. FIG. 1 is a sectional view of the main parts showing the implementation concept of the present invention,
Figure 2 is a sketch of the discharge side electrode, and 1 in the figure.
2 is a metal drum, 2 is an electrode hood, 3 is a discharge side electrode, 4 is a gas discharge pipe, 5 is a gas inlet, and 6 is a running film. That is, the film 6 is introduced from the direction of arrow B into the metal drum 1 rotating in the direction of arrow A, and is further pulled out in the direction of arrow C. , several hundred metal drums covered with polyester, epoxy resin, ceramic, chlorosulfonated polyethylene, EP rubber, etc.
Under the influence of the high-pressure corona generated by applying a high voltage of several thousand to tens of thousands of volts with the high frequency of KC/S, for example, in the natural atmosphere, ozone and nitrogen oxide are generated and the surface of the film 6 is affected. The surface becomes polarized by generating carbonyl or carboxyl groups on the surface. However, in this example, the entire corona discharge atmosphere is isolated from the atmosphere by the electrode hood 2, and an inert gas is introduced into the hood 2 through the opening 7 provided at the top of the electrode hood 2 to create an oxygen-free atmosphere. Further, since the discharge side electrode 3 is provided with a gas inlet 5 and configured to actively exhaust the atmospheric gas from the inlet 5 to the outside of the hood, various effects depending on the type of inert gas (for example, With N ₂ gas, it is possible to improve oxygen barrier properties due to the formation of nitrogen-containing groups, and with CO ₂ gas, it is possible to obtain further improvement in adhesiveness due to improvement in corona discharge efficiency. The illustrated discharge side electrode 3 is based on the concept of the second
As shown in the figure, a gas inlet 5 that opens toward the discharge surface is formed in the shape of a slit along the longitudinal direction of the electrode 3 (width direction of the film to be processed), and the bottom of the slit is provided with appropriate intervals. A gas exhaust pipe is connected to the gas exhaust pipe 5, and the end of the gas exhaust pipe 5 is connected to a gas suction pump (not shown).
In addition, appropriate cover plates may be attached to both longitudinal ends of the slit (the front side and the opposite side in the figure, however, the opposite side is not shown in the figure) for the purpose of preventing gas suction from the end faces. By the way, a small amount of entrained air layer is formed on the surface of the film 6 that enters at a fairly high speed along the direction of arrow B, and it is not possible to simply create an inert gas atmosphere inside the hood as in the past. However, the surface of the film 6 itself still retains the air atmosphere and cannot enjoy the effects obtained by the present invention. However, by adopting the above configuration, as shown in FIG. 3, on the film entry side of the discharge side electrode 3, the intake air flow _K1 to the gas intake port 5 is formed to be narrowed into a narrow discharge gap. The accompanying air layer 8 is drawn in and disturbed by the intake airflow K ₁ like an ejector, or the airflow K ₁
The suction pressure causes the discharge to be disturbed so that it protrudes in front of the discharge gap. Near the bottom of the gas inlet 5, the disturbed accompanying air layer sucked into the discharge gap is further disturbed as it opposes the intake airflow _K2 from the delivery side of the film 6, and together with both airflows _K1 and _K2 , the gas It is sucked into the suction port 5. In this way, the accompanying air layer 8
At the same time, it becomes possible to maintain at least half of the corona discharge area (the latter half of the film advance) as a complete inert gas atmosphere. Figures 4 to 10 are explanatory diagrams showing various structural examples of the discharge-side electrode used in the present invention and the behavior of the intake gas in the structures, and are not exhaustive examples, so they may be combined appropriately. This is left to the discretion of the person implementing the invention. Figure 4 shows the same structure as the electrode shown previously.
Inert gas (hereinafter simply referred to as gas) is inhaled as shown by the arrow. In the example shown in FIG. 5, the gas inlet is deflected in a direction opposite to the direction in which the film enters. As a result, the intake airflow from the inlet side (the left side in the figure) can easily flow into the gas inlet 5, and the entrained air layer can be more thoroughly stirred and removed than in the example shown in FIG. Furthermore, since the passage distance of the intake airflow from the outlet side (right side in the figure), in other words, the discharge area from which the accompanying air layer is removed becomes longer, corona discharge is performed better. FIG. 6 shows an example in which a gas collection electrode (hereinafter simply referred to as collection electrode) 3' made of a porous material such as a conductive metal sintered body or steel wool is added to the tip of the electrode 3. In this case, the collecting electrode 3' functions as a gas collecting port to the gas inlet 5, and gas is sucked in from the entire tip of the collecting electrode 3', collects at the gas inlet 5, and is discharged to the outside of the hood. Ru. Therefore, the accompanying air layer is removed smoothly and completely, resulting in the effect that the gas atmosphere in the corona discharge section is stabilized. In Figure 7, the electrode is divided into front and rear parts (left and right in the figure, the same below), with a gas collection electrode having the same configuration as in Figure 6 on the front side, and a normal electrode without a gas suction function on the rear side. These are integrated. This example was designed based on the idea of destroying and removing the accompanying air layer at the beginning of the approach, and in that sense it is the fifth example.
The same effect as the example shown is expected. Figure 8 shows an example in which the electrode is divided into three parts, the gas collection electrode of Figure 6 is placed in the center, and normal electrodes are placed at both front and rear ends.
FIG. 9 shows an example in which a normal electrode is arranged in the center and gas collection electrodes are arranged at both front and rear ends, and the configuration is completely reversed. However, both methods exhibit the same effect of destroying and removing the accompanying air layer and protecting the atmosphere of the corona discharge section. FIG. 10 shows an example in which a gas suction pipe 9 having an opening facing the film is provided on the film entrance side (left side in the drawing) of the electrode 3; gas flow K ₁ taken in from the left side)
Then, a gas flow K ₂ is formed which is normally drawn from the film delivery side of the electrode (right side of the drawing) through the discharge gap at the bottom of the electrode, and the accompanying air layer is agitated and dissolved by these air flows K ₁ and K ₂ . , exhibits the same effect as above. FIG. 11 shows an example in which two normal electrodes are installed independently of each other, and since the intake gas is discharged from between the electrodes to the outside of the hood, the inert gas flows in the direction shown in the figure. In each of the above embodiments, the downstream side of the electrode was explained as being flat, but it may be pointed at an acute angle or an obtuse angle.
It may be a hemispherical shape with roundness, or a shape in which these are repeated in two or more stages in the film passing direction (for example, a sawtooth shape, etc.), in short, the corona discharge of the plastic molding passing through it. Any electrode structure may be used as long as it is not inconvenient for forming an inert gas flow on the processing surface. Although the structure of the present invention is as described above, it is free to separately add means for enhancing the corona discharge treatment effect, and all such means are included in the present invention regardless of whether such means are known or not. As such a method, the plastic molding is exposed to corona discharge at the same time.
Alternatively, preheating is exemplified, and specifically, pretreatment with flame or, if the plastic molding is a long object such as a film, heating the long object by passing it through a temperature control roll beforehand is exemplified. It is recommended to preheat the drum or warm the metal drum itself. However, in the present invention, since the inert gas to be inhaled is preheated by contact with the electrode,
An extremely high corona discharge treatment effect can be obtained even without adding the above-mentioned means. Next, examples and comparative examples of the present invention will be described. A biaxially stretched film (thickness: 20 μm) of isotactic polypropylene (mixed with 0.6% by weight of polyoxyethylene alkylamine) was subjected to corona discharge treatment using the apparatus shown in FIG. The treatment conditions and results are shown in Table 1. As Comparative Example 1, corona discharge treatment was performed in the atmosphere (without nitrogen gas spraying), and as Comparative Example 2, corona discharge treatment was performed while nitrogen gas was injected into the electrode cover (but without nitrogen gas spraying). I did this. The respective treatment conditions and results are also listed in Table 1.

[Table] In the examples, high current was obtained even at the same voltage as in Comparative Examples 1 and 2, and extremely excellent results were obtained in terms of adhesive properties. In particular, clearly better results were obtained than in Comparative Example 2 (simple low-oxygen atmosphere). In addition, when we re-experimented the example and comparative example 2 by increasing the oxygen concentration in the electrode cover to 1%, the results in comparative example 2 were similar to those in comparative example 1, but the good results in the example were maintained. . Since the configuration of the present invention is as described above, various effects can be obtained as summarized below. (1) The atmospheric layer carried into the corona discharge treatment section along with the surface of the plastic molded article is stirred by the gas flow sucked into the opening provided on the side or bottom of the discharge side electrode, and the gas is At the same time, the gas is sucked into the gas inlet and discharged outside the hood, ensuring that it is destroyed and eliminated. Therefore, a discharge section in which air is not mixed can be reliably formed using a small amount of gas. (2) As a result, the current value and power value per unit area increase dramatically, and the corona discharge treatment effect improves by increasing the effective power density. (3) Also, the unique effects of the atmosphere of the cloth, e.g.
Due to the presence of N ₂ gas, the effect of forming amino groups and imino groups on the surface of plastic moldings (improving oxygen barrier properties), etc. is exhibited to an extremely high degree.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram showing the implementation status of the present invention, Figure 2
The figure is a sketch of the discharge side electrode used in the present invention,
FIG. 3 is an explanatory diagram showing how the accompanying air layer is destroyed and resolved, and FIGS. 4 to 11 are explanatory diagrams illustrating the flow of electrodes and gas used in the present invention. 1...metal drum, 2...electrode hood, 3...
Discharge side electrode, 4... Gas exhaust pipe, 5... Gas inlet, 8... Associated air layer, 9... Gas inlet pipe.

Claims (1)

[Claims] 1. When carrying out corona discharge treatment by continuously carrying plastic molded articles into a corona discharge treatment apparatus in which at least one pair of electrodes are arranged facing each other and the discharge side electrode is surrounded by a hood,
A gas body excluding air and oxygen is introduced into the hood, and corona discharge is performed while actively exhausting the gas body from the side or bottom surface of the discharge side electrode to the outside of the hood along the current direction of the discharge side electrode. 1. A corona discharge treatment method for plastic molded articles, characterized by carrying out treatment.