JPH0225935B2 - - 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 VOL15
PP1365-1375 (1971) describes 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 in place of the atmosphere have also been proposed, but conventional methods, such as the method disclosed in Japanese Patent Publication No. 18381/1983, require a large amount of inert gas, leading to high costs. There are some problems, and the method of JP-A-57-23634 (corona discharge technology under inert atmosphere for running film)
In this case, a special shield structure is required to block the atmosphere that is entrained by the film, which complicates the equipment. A completely inert atmosphere was not created and low treatment levels had to be settled. 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 method in which a plastic molded article is continuously carried into a corona discharge treatment apparatus provided with at least one pair of opposing electrodes and subjected to corona discharge treatment. From the side wall surface or bottom surface of the side electrode to the treated surface of the plastic molding, a single or mixed gas with an oxygen concentration lower than that of the air [specifically, a gas from which an appropriate amount of oxygen has been removed from the air composition, or a gas containing oxygen from the air] Those with an appropriate amount of other gases added, and even
The corona discharge treatment is performed while spraying gases such as B ₂ , H ₂ , Ar, CO ₂ , etc. alone or in combination (hereinafter referred to as low oxygen concentration gas), and this spraying speed is The gist of this is that it is set at 1% or more of the above-mentioned plastic molded article conveyance speed. 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 structure 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 and the shape of the cover shown in the drawings are only representative examples. Since the above is merely an example of application to plastic film, it is within the technical scope of the present invention to change the design as long as 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,
FIG. 2 is a perspective view showing a part of the discharge side electrode, in which 1 is a metal drum, 2 is an electrode cover 3 is a discharge side electrode, 4 is a gas supply pipe, 5 is a gas outlet,
6 indicates 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. , polyester, epoxy resin,
Ceramic, chlorosulfonated polyethylene,
Under the influence of high-pressure corona generated by applying a high voltage of several thousand to tens of thousands of V at a high frequency of several hundred KC/S between the metal drum 1 covered with EP rubber etc. If it is inside, ozone and nitrogen oxide are generated to generate carbonyl groups and carboxyl groups on the surface of the film 6, thereby polarizing the surface. However, in this example, the entire corona discharge atmosphere is isolated from the atmosphere by the electrode cover 2, and a gas outlet 5 is provided on the discharge side electrode 3 to blow low oxygen concentration gas toward the surface of the film 6. Since the structure _is composed of Improved processing efficiency by expanding the effective discharge area of CO ₂ gas, it is possible to obtain further improvements in adhesion by improving corona discharge efficiency. The concept of the illustrated discharge side electrode 3 is that, as shown in FIG. Gas supply pipes 4 are connected to the bottom of the slit at appropriate intervals.
Therefore, the low oxygen concentration gas supplied under pressure through the gas supply pipe 4 is dispersed in the longitudinal direction within the slit section and is ejected almost uniformly from the gas outlet 5, so that the atmosphere in the corona discharge section becomes a low oxygen concentration gas. Replaced. In addition, appropriate cover plates may be attached to both sides of the slit in the longitudinal direction (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 diffusion from the end face. However, a slight accompanying air layer is formed on the surface of the film 6 that enters at a considerably high speed in the direction of arrow B, and the atmosphere in the corona discharge area is replaced by low oxygen concentration gas. However, the surface of the film 6 itself still retains the atmospheric atmosphere, and the effects of the present invention cannot be enjoyed if the low oxygen concentration gas is simply spouted out aimlessly. Therefore, low oxygen concentration gas is used as a third
We believe that if the accompanying air layer 7 is destroyed and dispersed by the jet flow 8 by ejecting it strongly as shown in the figure, the atmosphere in the corona discharge area can be almost completely replaced by low oxygen concentration gas. Various considerations were made. As a result, it was found that the intrusion speed of the accompanying air layer 7 is an important factor, and it is at least 1% or more, preferably 10% or more, and more preferably If a jet stream 8 is formed at a speed of 40% or more,
It has been found that the accompanying air layer can be destroyed and dispersed to the extent that there is no practical problem. Furthermore, the conveyance speed of plastic moldings is generally 1~
500m/min. By adopting such conditions, it becomes possible to destroy and disperse the accompanying air layer, and at the same time, it becomes possible to protect the vicinity of the corona discharge part with a low oxygen concentration gas atmosphere. The electrode cover 2 shown in the figure is expected to have a function of protecting the electrode 3 from mechanical shock and suppressing the accompanying flow even slightly, rather than a function of maintaining the atmosphere. . Therefore, when implementing the present invention, the electrode cover 2 may be removed from time to time, but in order to suppress the consumption of low oxygen concentration gas, it is desirable to reconsider its function for maintaining the atmosphere. For example, as shown in FIG. 4, if the lower end (film side) of the cover 2 is squeezed and at the same time low oxygen concentration gas is introduced into the cover 2 from the conduit 10, the gas will be converged along the inner surface of the slope 9. The gas flows in the direction of the arrow, and a gas curtain effect is exerted at the inlet of the cover 2. That is, the intrusion of the entrained air layer is blocked on the inlet side, and the value of the electrode cover 2 is further improved. However, on the exit side of the film 6 (the right side in Fig. 4), the gas inside the cover 2 is discharged along with the traveling film 6, so the sealing performance or air infiltration barrier properties should be given the same consideration as on the entrance side. Although it is not necessary, it is meaningful to take the same consideration as on the inlet side in terms of reducing the amount of low oxygen concentration gas consumed as described above. In order to achieve the above-mentioned sealing function on the inlet and outlet sides of the cover 2 to the minimum extent, the pressure should be at least 0.2% or more relative to the film running speed.
It is desirable to release it onto the film surface preferably at a rate of 10% or more. Regarding the ejection speed of low oxygen concentration gas, only the lower limit side has been described for both the gas ejection port 5 and the inlet/outlet of the cover 2, but there is no practical need to set an upper limit on the ejection speed, and at most the ejection amount and ejection effect are limited. From the standpoint of budget and economy, the former should be 10 times or less, preferably 5 times or less, the traveling speed, and the latter should be 10 times or less, preferably 5 times or less, the traveling speed. Figures 5 to 25 are explanatory diagrams showing various structural examples of the discharge side electrode used in the present invention and the behavior of the ejected gas in the structures, and are not meant to exhaustively show the examples, so they may be combined appropriately. This is left to the discretion of the person implementing the invention. Figure 5 shows the same structure as the electrode shown previously.
Low oxygen concentration gas (hereinafter simply referred to as gas) is ejected in the direction of the arrow. In the example shown in FIG. 6, the gas outlet 5 is placed on the inlet side (in the figure) so as to face the direction in which the film enters, or in other words, to blow gas directly against the entry of the accompanying air layer on the film. left)
is biased towards. It is also useful to flow the gas along the inlet and outlet (right side in the figure) sides of the electrode 3 as shown by arrows D and E. Fig. 7 shows a gas diffusion electrode (hereinafter simply referred to as diffusion electrode) 3' made of a porous gas diffusion material such as conductive metal sintered steel wool or wire mesh added to the tip of the electrode 3. This is an example. In this case, the gas ejection port 5 functions as a gas supply port to the diffusion electrode 3', and gas is ejected from the entire tip of the electrode. Therefore, the gas is ejected smoothly and the gas atmosphere in the corona discharge section is stabilized. FIG. 8 is an example in which formation of a gas flow along the electrodes is added to the example of FIG. 7. In Fig. 9, the electrode is divided into front and rear (left and right in the figure, the same below), and a gas ejection electrode with the same configuration as Fig. 7 is placed on the front side, and a normal electrode without a gas ejection function is provided on the rear side. These are integrated. This example was designed based on the idea of destroying and diffusing the accompanying air layer at the beginning of the approach. Figure 10 shows the electrode divided into three parts.
An example in which a gas ejection electrode as shown in Fig. 7 is provided in the center and normal electrodes are arranged at both front and rear ends, and Fig. 11 is an example in which a normal electrode is arranged in the center and gas ejection electrodes are arranged at both front and rear ends. The composition is exactly the opposite. However, both methods exhibit the same effect of destroying and diffusing the accompanying air layer and protecting the atmosphere of the corona discharge section. FIG. 12 shows an example in which the central normal electrode in FIG. 11 is provided with a gas outlet 5 having the same configuration as that in FIG. 5, and the above effect is even more pronounced. FIG. 13 shows gas jet pipes 11 in front and above the electrode 3.
In this example, the gas ejected directly below from the pipe 11 descends along the electrodes, producing the same effect as described with reference to FIG. In the examples shown in FIGS. 6, 8, and 13, the gas is ejected in a concentrated manner through the pipe 11, so that a small amount of gas can be effectively utilized. Figures 14 to 22 show examples of a method in which gas is ejected on one side and sucked on the other side.As far as the gas is ejected, there is no difference from the previously described examples, but this gas is Since it is sucked in from other parts, firstly, the ejected gas is forcibly moved in a specific direction, which strengthens the protection of the corona discharge area, and secondly, a part of the ejected gas is recovered, and in some cases In addition, a part of the gas can be mixed and reused in the ejected gas as it is, so that effects such as reduction in gas cost can be obtained. However, if the pressure on the suction side falls below atmospheric pressure, there is a risk that the accompanying air layer will be drawn directly to the lower end of the electrode, so it is necessary to maintain the pressure above atmospheric pressure. First, Fig. 14 shows an example in which one side is a gas jet port 5 and the other side is a gas suction port 5'.
A part of the gas ejected from the former is consumed to destroy and disperse the accompanying air layer, and the remaining part travels on the film to form an atmosphere in the corona discharge area and is then recovered from the gas suction port 5'. Figure 15 shows the spout 5,
Example of adding sintered metal to the suction port 5', No. 16, 1
FIG. 7 corresponds to FIGS. 11 and 12 and is an example in which gas is ejected and sucked as shown in the figures, and each of the above-mentioned effects is fully exhibited in both cases. Figure 18 shows plates 12, 12 before and after the electrode 3.
This is an example in which the plates 12 are disposed close to each other, and the lower end of the plate 12 is bulged and the gas ejection pipe 11 is disposed. Then, when gas is ejected from the pipe 11 while sucking the space between the electrode 3 and the plate 12 from above to form an upward gas flow, a part of the ejected gas is released from the aforementioned bulge. Particularly on the inlet side, the accompanying air layer is destroyed and diffused. The remaining portion covers the lower surface of the electrode 3 or is sucked vertically upward. Figure 19 shows the 14th electrode in the center of electrode 3.
An example in which a gas suction port 5' similar to that shown in the figure is formed, No. 20
The figure shows an example in which sintered metal is attached to the front side, and Figure 21 shows an example in which a plate 12 is provided only on the inlet side.
In this example, gas is ejected from the gap between the two electrodes 3 and also from the entire bottom surface of the electrode 3, while the gas suction pipe 14 is exposed to the bulge of the plate 12 to suck the ejected gas. Then, a part of the entrained air layer is forced into the suction tube 14. 22nd
The figure shows a modification of FIGS. 12 and 17, in which a sintered metal is added to the tip of the gas electrode 3, which was originally integrated, and the gas outlet 5 in the center is formed by penetrating it to the tip of the sintered metal. The side gas suction port 5' is stopped in front of the sintered metal. The gas that exits the spout 5 flows as shown by the arrow and is recovered from the suction port 5'.
Finally, the gas may be ejected from the suction port 5' side and the gas may be sucked from the ejection port 5 side. Figures 23 to 25 show examples in which two electrodes are installed independently and side by side. It is recommended to make each of the above-mentioned effects even more remarkable by using the following. First, Fig. 23 shows an example in which two unprocessed electrodes are placed close together, and the gap between them is used as a slit to flow the gas downward, and the gas is ejected as shown in the figure. , 23 is applied, and the gas suction port pipes 14 in FIG. 21 are arranged on both sides of the electrode. Finally, FIG. 25 shows the electrodes in FIG. 7 and the electrodes in FIG. 6 in the gas suction gap 15.
This is an example of two pipes being lined up so as to leave a gap, and the ejected gas flows in the direction shown by the arrow. In each of the above embodiments, the lower end 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 a rounded shape, 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 shape of the plastic molded object passing through Any electrode structure may be used as long as it does not cause any inconvenience in spraying the low oxygen concentration gas onto the corona discharge treated surface. Although the structure of the present invention is as described above, it is free to add additional means for enhancing the effect of corona discharge treatment. Examples of such means include heating the plastic molding at the same time as the corona discharge or in advance of the corona discharge. If the object is a long object, it is recommended to preheat it through a temperature control roll or warm the metal drum itself. However, in the present invention, since the low oxygen concentration gas to be sprayed is sufficiently 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 addition, surface analysis of the untreated film and the treated film was performed by ESCA analysis (electron spectroscopy for chemical analysis), and the results shown in Table 2 were obtained. Measurement of (N/C) ratio and (O/C) ratio by ESCA method Using an ESCA spectrometer (ES-200 model: manufactured by Kokusai Denki Co., Ltd.), carbon on the film surface was measured.
The integrated intensity obtained from the 1s orbital spectrum and the nitrogen
Calculate the ratio of the integrated intensity obtained from the peak corresponding to the binding energy of organic nitrogen from the 1s orbital spectrum, calculate the number of nitrogen per 100 carbons based on the integral ratio, and calculate this value as (N/C ) ratio. The ratio of carbon to oxygen on the film surface was similarly expressed as the number of oxygen per 100 carbon atoms as the (O/C) ratio.

[Table] As shown in Table 2, in Comparative Examples 1 and 2 (O/
C) ratio is high and removal of air from the film surface is insufficient, whereas in Examples the (O/C) ratio is significantly lower. In the example, the (N/C) ratio after treatment effectively increases and [Δ(O/
C)/Δ(N/C)] is also a low value of 1.09 (indicating excellent adhesion). In other words, based on the results in Table 2, it is only by spraying low oxygen concentration gas onto the film surface that the accompanying atmosphere on the film surface can be removed, simply creating a low oxygen concentration gas atmosphere inside the electrode cover (comparative example). It was confirmed that 2) alone does not remove the entrained air. Thus, as shown in Tables 1 and 2, in the example, a 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 the oxygen concentration in the electrode cover was increased to 1% and both the Example and Comparative Example 2 were tested, 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 reliably destroyed and dispersed by the low oxygen concentration gas sprayed onto the surface. Therefore, it is extremely unlikely that air will be mixed into the atmosphere of the corona discharge area.
Even if the amount of gas is small, the desired atmosphere is reliably formed. (2) On the other hand, since the blown gas has a lower oxygen concentration than the atmosphere, the atmosphere is emitted from the corona discharge atmosphere and the residual concentration is low.
The oxygen concentration in the discharge atmosphere becomes low. (3) Therefore, by discharging uniformly over the entire surface of the electrode, the effective electrode area is expanded, and the current value and power value per unit area are increased. In other words, the current increases dramatically even under the same voltage, and the corona discharge treatment effect improves due to the increase in effective power density. (4) Also, the unique effects of each atmosphere, 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. (5) As shown in Table 2, the method of the present invention can reduce the amount of O ₂ attached to the film surface,
It is possible to obtain discharge treatment effects (improvement in adhesion, etc.) that cannot be achieved with a simple inert gas atmosphere.

[Brief explanation of drawings]

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 the state of destruction of the accompanying atmospheric layer, Fig. 4 is an explanatory diagram showing an example of the electrode cover, and Figs.
FIG. 5 is an explanatory diagram illustrating the electrodes used in the present invention and the flow of ejected gas. DESCRIPTION OF SYMBOLS 1...Metal drum, 2...Electrode cover, 3...Discharge side electrode, 5...Gas outlet.

Claims (1)

[Claims] 1. When plastic moldings are continuously carried into a corona discharge treatment device comprising at least one pair of electrodes facing each other and subjected to corona discharge treatment, plastic molding is carried out along the side wall surface of the discharge side electrode or from its bottom surface. towards the corona discharge treated surface of the object.
A method for corona discharge treatment of the surface of a plastic molded article, characterized in that the corona discharge treatment is carried out while blowing a gas having a lower oxygen concentration than air at a speed of 1% or more of the conveyance speed of the plastic molded article.