JPH1067869A - Corona discharge treatment method for plastic surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a large-size plastic molding to be uniformly treated in a short time with a small-size power source by subjecting the surface of the molding to corona discharge generated by applying a specific high-voltage pulse while exposing the surface to a gas stream. SOLUTION: A plastic molding 3 to be treated is placed between a corona discharge electrode 1 and a counter electrode 2. The angle (a) between a perpendicular line from the discharge electrode 1 toward the counter electrode 3 and a straight line connecting the air blow port 5 of an air blow pipe 4 to the point of intersection C is set at 0-90 deg., and the distance d between the port 5 and the point of intersection C is set at 1-40cm. A gas is blown from the port 5 to the surface of the molding 3 at a blow rate of 0.05-40L/min.cm<2> , A high- voltage pulse with a pulse width of 1 βgsec or higher, an average electric field strength, expressed by applied voltage (crest value)/distance between electrodes, of 4-20 kV/cm, and a pulse frequency of 20pps or higher is applied to the discharge electrode 1, and the generated corona discharge is used for treating the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for corona discharge treatment of a plastic surface.

[0002]

2. Description of the Related Art A method for treating a plastic surface by corona discharge to improve its surface properties has been known for a long time. In order to obtain a uniform processing effect even on a resin molded product having three-dimensional irregularities, that is, a three-dimensional shape, Japanese Patent Laid-Open No.
Various methods are disclosed in, for example, JP-A-7-119931 and JP-A-62-57431. However, in these corona discharge treatments, spark discharge is likely to occur, and there is a drawback that sufficient treatment is difficult to reach the edge of the resin molded product where the inner periphery of the outer peripheral opening exists. In these prior arts, a corona discharge generated by an AC high-frequency voltage has generally been used. Further, Japanese Patent Application Laid-Open No. 58-225133 discloses a method of performing corona discharge treatment while blowing gas onto a plastic surface. This method is characterized in that an amino group or an imino group is formed on a plastic surface by using a gas other than air and oxygen as a blowing gas. However, this does not include the idea of using corona discharge with high voltage pulses. JP 6
In Japanese Patent Application Laid-Open No. 2-149731, air blowing is combined with contact corona discharge processing in which the discharge electrode is in contact with the surface of the object to be processed, but the processing range cannot be widened.

[0003] Japanese Patent Application Laid-Open No. 5-33997 discloses a method of treating a plastic surface by generating a corona discharge by a high voltage pulse. Although this method is useful for industrially treating a molded article having a three-dimensional shape, it is still not enough to impart a surface treatment effect, particularly sufficient hydrophilicity to a plastic surface. That is, in the case of a plastic molded body having a three-dimensional structure, if an attempt is made to treat the peripheral portion of the molded product or the inner peripheral portion of the opening using an AC high-frequency voltage, the distance between the discharge electrode and the counter electrode becomes small, so that the air layer Spark discharge due to dielectric breakdown of the substrate. On the other hand, if a high-voltage pulse with a narrow pulse width is used, spark discharge is unlikely to occur, but if an attempt is made to increase the processing effect using a high-voltage pulse with such a narrow pulse width, a high applied voltage is required, and energy efficiency is reduced. Extremely low. Further, in the present invention, since there is no ventilation, the processing effect is not sufficiently large. In the above conventional corona treatment, it takes a long time for the treatment or requires a large power supply to perform the modification to give sufficient adhesion to the plastic surface, which is industrially suitable. Not. In addition, there is a disadvantage that the processing of a complicated shape portion (for example, a groove portion) of a large molded product cannot be uniformly processed.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a corona discharge treatment method capable of overcoming the above-mentioned drawbacks and uniformly treating a large molded product in a reasonably short processing time by using a small power source. That is. This is intended to improve the surface of plastic having poor wettability and improve the applicability, printing characteristics, adhesiveness, and the like of a fluororesin or the like.

[0005]

According to the present invention, a pulse width of 1 μsec or more is applied while exposing a plastic surface to a gas flow.
Corona discharge treatment in a discharge region in which a corona discharge is generated by applying a high-voltage pulse having an average electric field strength expressed by an applied voltage (peak value) / inter-electrode distance of 4 to 200 kv / cm and a pulse frequency of 20 pps or more. The present invention relates to a method for treating a plastic surface.

The present invention is characterized in that, when corona discharge is performed on a plastic surface, (1) the corona discharge is performed by a high voltage pulse while (1) the plastic surface is exposed to a gas flow. Sending an air current to stabilize the plasma state is a known technique, but the high-frequency corona discharge could not expand the effective plasma area even in combination with blowing. However, in the present invention, corona discharge by pulse voltage is used, and therefore, it is possible to widen a plasma region that can be subjected to corona discharge treatment by blowing air, and to more uniformly and effectively treat an object to be treated. Is possible.

The plastic modified by the present invention is a polyolefin such as polyethylene (high-density polyethylene,
Medium density polyethylene, low density polyethylene, high pressure polyethylene, medium pressure polyethylene, low pressure polyethylene,
Linear low-density polyethylene, branched low-density polyethylene,
High-pressure normal low-density polyethylene, ultra-high-molecular-weight polyethylene, cross-linked polyethylene, polyethylene modified with a small amount of modifying monomers, etc.), polypropylene, modified polypropylene, polyisobutylene, polyisoprene, polybutadiene, their copolymers, polyolefin mixtures, Mixtures of polyolefin and polyvinyl chloride, polystyrene, polycarbonate, etc., fluororesins such as ethylene-tetrafluoroethylene copolymer (ETFE), polyvinyl fluoride resin (PVF), tetrafluoroethylene-perfluoroether copolymer (PFA) , Tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytetrafluoroethylene (PTF)
E), vinylidene fluoride resin (PVdF), trifluorochloroethylene resin (PCTFE), ethylene-trifluorochloroethylene copolymer resin (ECTFE), etc., are plastics that are themselves strongly hydrophobic and hard to wet with water. These plastics may also contain additives such as pigments, fillers and lubricants.

These plastics may have a planar structure such as a film, a sheet or a panel, or may be a tube, a pipe, or a molded article having a three-dimensional structure having irregularities. In particular, the present invention is characterized in that it can be effectively applied to a molded article having a three-dimensional structure having irregularities.

The plastic to be treated according to the present invention is inserted between the discharge electrode for corona discharge and the counter electrode, and performs corona discharge while flowing gas to the surface of the plastic.

In the present invention, the gas refers to oxygen, nitrogen, or a rare gas such as helium or argon, and one or a mixture of two or more of them is selected according to an object to be processed. For example, for a fluororesin whose surface modification is difficult, helium and oxygen are mixed and used.

The gas causes the plastic surface to flow as a gas stream. In particular, corona discharge occurs while spraying on the plastic surface. The spraying conditions are as follows. As shown in FIG. 1, when a plastic to be treated (3) is arranged between a discharge electrode for corona discharge (1) and a counter electrode (2), a point at which a perpendicular from the discharge electrode to the counter electrode intersects the surface of the plastic to be treated. It is good to blow gas toward (c),
The blowing angle (α) (the angle between the perpendicular from the discharge electrode to the counter electrode and the straight line connecting the blowing port (5) and the intersection (c)) is 0 to 90.
Degrees, preferably 0 to 45 degrees, more preferably 0 to 30 degrees.
Degree, the blowing distance (d) (the distance between the blowing port and the intersection (c)) is 1 to 40 cm, which is set according to the distance between the tip of the discharge electrode and the surface of the workpiece and the shape of the workpiece. It is.

Under these conditions, the amount of gas blown depends on the blow angle (α) and the blow distance (d).
0.05 to 40 L / min · cm ² , preferably 0.2 to 40 L / min · cm ²
30 L / min · cm ² , more preferably 0.4 to 8 L /
min · cm ² is appropriate. If the blowing angle (α) is 90 degrees or more, it is difficult to blow air into the discharge region, and the surface modification effect is not sufficient. When the blowing distance (d) is 15 cm or more, the wind pressure of the gas hitting the surface of the plastic to be treated becomes low,
At the time of corona discharge, the contact efficiency or permeability between the plastic surface and the active gas becomes low, and the surface modification effect becomes insufficient. If the gas blowing rate is less than 0.05 L / min · cm ² , the blowing effect becomes insufficient, and 40 L / min · c
If it is larger than m ² , the corona discharge itself is diffused, and the surface modification effect is impaired.

FIGS. 2 and 3 show a typical example of a device (blower pipe) which can be used for blowing gas which can be used in the present invention. FIG. 2 is a sectional view of the blower pipe, and FIG. 3 is a front view of the blower pipe. (4) is a blower pipe, (5)
Denotes a blow port and (7) denotes a blow nozzle. The diameter of the blowing pipe (4) is suitably 20 to 40 mm. If the diameter is larger than this, the pipe contacts the discharge electrode. The length of the blowing nozzle is 0 to 40 mm, and the length of the blowing port is 200 to 100
0 mm, especially 300-800 mm, is suitable. This length may be determined in accordance with the size of the discharge electrode. The width of the blowing port is preferably 0.5 to 10 mm, particularly 0.5 to 5 mm. When there are a plurality of discharge electrodes, a blowing port may be provided for each discharge electrode. FIG. 4 shows one embodiment of the present invention in which a discharge electrode and a blower pipe are integrated with each other so that blown air can be more efficiently blown to the surface of an object to be processed. In addition, the selection of the relationship between the discharge electrode and the blowing pipe can be performed according to the shape of the object to be processed.For example, when the object to be processed is a film or a block having a simple surface shape, , An integral type is preferred. On the other hand, when the object to be processed has a complicated shape, it is preferable that the blower pipe is separate from the discharge electrode. The above embodiment is merely an example of the spraying device of the present invention,
It is not limited to this.

The corona discharge used in the present invention is performed by high voltage pulses. The pulse width is 1 μsec or more. Conventionally, it was thought that the pulse width had to be 1 μsec or less in order to perform the corona discharge treatment without sparking. However, under the discharge conditions (average electric field intensity, pulse frequency) as in the present invention, the treatment of the plastic surface was difficult. Harmful sparks are hardly generated, and the effect of blowing gas is remarkable. If the pulse width is less than 1 μsec, the surface treatment effect of the plastic is not sufficiently performed, and the energy efficiency is reduced to sufficiently perform the effect.

On the other hand, as the pulse width increases, the effective discharge energy increases, so that the surface treatment effect on the plastic molded product increases. Alternatively, the corona discharge will extend far away on the surface of the plastic molding.
That is, the processing efficiency is improved, and the desired surface treatment effect can be achieved in a short time. In addition, when the pulse width is large, even if the distance between the poles is increased, a corona discharge of sufficient strength can be generated and a good surface treatment effect can be achieved. Thus, there is no need to dispose each electrode. Therefore, the discharge electrode can be arranged at a position away from the plastic molded product by using the counter electrode and the discharge electrode having simpler shapes. As a result, even for a plastic molded product with a complicated shape, a relatively simple electrode shape can be adopted,
It is not necessary to change the shape of each electrode for each molded product.

However, if the pulse width is too long, harmful sparks are likely to occur and the power supply capacity increases.
It is preferably set to 0 μsec or less. Preferably, the pulse width is 1 to 50 μsec, more preferably 1 to 30 μsec.
c.

The discharge phenomenon is also affected by the distance between the electrodes and the applied voltage. The distance between the electrodes refers to the distance between the discharge electrode and the counter electrode, and specifically, is preferably 5 to 400 mm. Particularly, when processing a large molded product, it is necessary to enlarge the processing area, and therefore, it is preferably 50 to 400 mm.

The applied voltage for corona discharge is 4 to 200 expressed as the average electric field strength (applied voltage (peak value) / distance between electrodes).
kv / cm, preferably 6 to 150 kv / cm, more preferably 8 to 120 kv / cm. Average electric field strength 4
If it is less than kv / cm, effective corona discharge hardly occurs,
The surface treatment effect is poor. Average electric field strength is 200kv
If it exceeds / cm, sparks are likely to occur, and both are not preferred.

When the applied voltage is relatively high and the average electric field strength is 6 kv / cm or more, it is desirable to interpose a dielectric (6) described later between the counter electrode and the plastic.

The pulse frequency is 20 pps or more, preferably 20 to 1000 pps, more preferably 40 to 700 pps.
ps. If the pulse frequency is less than 20 pps, the effective treatment energy per unit time is insufficient, and the surface treatment time is long, which is not preferable. It is technically difficult to generate a high voltage pulse having a pulse frequency exceeding 1000 pps with a pulse width and an average electric field strength as described above. 10
It is not preferable to obtain a pulse frequency of 00 pps or more because the high-voltage generator becomes very large, the equipment cost becomes excessive, and industrial profitability cannot be obtained.

As the high-voltage pulse generator, basically, a high-voltage pulse generator in a conventional corona discharge treatment method can be used.

Preferably, a dielectric (6) is interposed between the counter electrode and the plastic to be processed. In this way, even when the applied voltage (peak value) is high and the average electric field strength is high, generation of harmful sparks can be prevented. As the dielectric, a vinyl chloride resin, a Teflon resin, and other general dielectric materials can be arbitrarily used. The thickness of the dielectric is 1 mm or more, preferably in the range of 5 to 20 mm. If the thickness of the dielectric is less than 1 mm, the spark preventing effect is insufficient. Even if the thickness is more than 20 mm, there is no difference in the effect of the treatment. The position of the dielectric is not particularly limited, and can be installed at any position. When a relatively thin dielectric layer is formed on the surface of the opposing electrode, the opposing electrode should be 0.1 in order to obtain sufficient mechanical strength and durability.
mm or more, desirably 1.6 mm or more is preferably used. A thin film or foil of a conductive material such as copper or aluminum formed on the back surface of the dielectric may be used as the counter electrode. In this case, it is preferable that the thickness of the dielectric is set to be relatively large, for example, about 5 mm or more in order to have mechanical strength. In order to perform corona discharge treatment continuously and uniformly, it is preferable to convey the plastic to be treated at a constant speed.

By the above-mentioned treatment, the surface of the plastic is made hydrophilic over a wide area in a shorter time than in the ordinary corona discharge treatment, and the wettability to water is improved.

Although the method of the present invention may be applied to flat surfaces such as plastic films, plastic sheets, and plastic panels, it is particularly useful for plastic molded articles having a three-dimensional structure.

Hereinafter, the present invention will be described with reference to examples. Example 1 A panel made of polypropylene (length 10 cm × width 5 cm × thickness 0.3 cm) was placed in a corona discharge device shown in FIG. 6 equipped with a 5 mm-thick vinyl chloride sheet as a dielectric. Was placed at a position where the blowing distance and the distance between the electrodes became 50 mm, and corona discharge treatment was performed under the following conditions.

Gas blowing conditions : The gas shown in Table 1 was blown at a rate of 2.5 L / min.
It was sprayed continuously on the panel in cm ² .

Corona discharge conditions : The panel was applied at a voltage of 150 KV and a pulse frequency of 100 pp under the above gas blowing conditions.
s and a distance between the electrodes of 50 mm were subjected to a corona discharge treatment for 60 seconds. The discharge electrode was 300 mm long and was arranged in parallel with the longitudinal direction of the air outlet.

Evaluation of wettability : The wettability of the panel subjected to corona discharge treatment to water was measured using a CA-D contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd.). As measurement points, a point directly below the discharge electrode and a point away from it by a distance D (perpendicular to the center line of the panel) were selected. Table 1 shows the measurement results.
Shown in Table 1 shows, as a comparative example, those subjected to corona discharge treatment under the same conditions as above without blowing gas.

[0029]

[Table 1]

Example 2 Tetrafluoroethylene perfluoroether copolymer (PFA) film (length 10 cm × width 5 cm × thickness 40)
μ) was placed in the same corona discharge device as in Example 1 at a position where the distance of air flow from the center of the panel and the distance between the electrodes were 20 mm, and corona discharge treatment was performed under the following conditions.

Gas blowing condition : The gas shown in Table 2 was blown at a rate of 2.5 L / min.
It was sprayed onto the film continuously in cm ² .

Corona discharge conditions : An applied voltage of 100 KV and a pulse frequency of 100 pp under the above gas blowing conditions.
6 at s and 500 pps and 20 mm between poles
Corona discharge treatment was performed for 0 seconds. The discharge electrode was 300 mm long and was arranged in parallel with the longitudinal direction of the air outlet.

Table 2 shows the contact angle measurement values obtained in the same manner as in Example 1 for the film subjected to the corona discharge treatment under the above conditions and for the film subjected to the corona discharge treatment without blowing gas as a comparison. did.

[0034]

[Table 2]

Example 3 Corona discharge treatment was performed in the same manner as in Example 2 except that the types of gas and the amount of air blown were as shown in Table 3. In addition, the contact angle measurement point was only the point immediately below the discharge electrode.

[0036]

[Table 3]

Example 4 A U-shaped product made of polypropylene as shown in FIG.
(Length 10cm x width 2cm x thickness 0.3cm, height Tcm)
Was placed in a corona discharge device shown in FIG. 1 equipped with a 5 mm thick sheet of vinyl chloride as a dielectric.

Gas blowing conditions : A blowing pipe for blowing gas (blowing port: width 5 mm, length 800 mm, blowing nozzle length: 40 mm), and a center line in the vertical direction of the bottom surface of the object to be processed just below the discharge electrode. Was passed, the gas was placed at a position where the blowing angle was 20 degrees and the blowing distance was 100 mm, and the gas shown in Table 4 was continuously blown onto the U-shaped object at a blowing rate of 5 L / min · cm ² .

Corona discharge conditions : The applied voltage was 230 KV, the pulse frequency was 85 pps, and the distance between the electrodes was 350 mm.
The discharge electrode is 35 ° in a direction perpendicular to the direction in which the object is transported.
Five pieces are arranged at 0 mm intervals so that the discharge length becomes 800 mm, and the object to be processed is transported under this at a conveying speed of 0.8 m / mi.
n.

Under the above conditions, various U-shaped objects having the height T shown in Table 4 were subjected to corona discharge treatment, and the contact angles at the center of the bottom surface were measured. The results are shown in Table 4.

[0041]

[Table 4]

[0042]

According to the present invention, the wettability of the plastic surface with water is improved by subjecting the plastic surface to a corona discharge treatment by a pulse voltage while blowing the gas onto the plastic surface. This makes it possible to improve the surface paintability and the like without changing the properties of the plastic itself. The wettability is related to the amount of air blow and can be uniformly processed over a wide range by blowing air.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a positional relationship among a discharge electrode, a counter electrode, an object to be processed, and a blowing pipe.

FIG. 2 is a sectional view of a blower pipe.

FIG. 3 is a front view of a blower pipe.

FIG. 4 is a configuration diagram of a discharge electrode and a blower pipe when the discharge electrode and a blower pipe are integrated.

FIG. 5 is a detailed view of the tip of the discharge electrode of FIG. 4 including a section taken along line XX '.

FIG. 6 is a schematic diagram showing a positional relationship among a discharge electrode, a counter electrode, an object to be processed, and a blow pipe when the discharge electrode and the blow pipe are integrated.

FIG. 7 is an overall view of a U-shaped object used in Example 4.

[Explanation of symbols]

1 discharge electrode, 2 counter electrode, 3 workpiece, 4
Blower pipe, 5 Blower port, 6 Dielectric, 7 Blower nozzle C Position where the perpendicular from the discharge electrode to the counter electrode crosses the surface of the workpiece, d Distance from blower pipe tip to point (c) (Blowing distance) α discharge The angle (blast angle) formed by the perpendicular from the electrode to the counter electrode and the straight line connecting point (c) to the tip of the blower pipe, L Length of blower port T Height of U-shaped object

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29K 27:12 (72) Inventor: Akunitsu Akeno Osaka Ikenagawa-city Ikedanaka-cho 19-17 Nippon Paint (72) Inventor Yasuyuki Tsuchiya 19-17 Ikedanakacho, Neyagawa-shi, Osaka Nippon Paint Co., Ltd.

Claims (6)

[Claims] An average electric field intensity expressed by an applied voltage (peak value) / electrode distance of 4 to 200 kv / cm while a plastic surface is exposed to a gas flow while a pulse width is 1 μsec or more,
A method for treating a plastic surface in which a corona discharge treatment is performed in a discharge region in which a corona discharge is generated by applying a high voltage pulse having a pulse frequency of 20 pps or more. 2. The plastic is a polypropylene resin,
2. The treatment method according to claim 1, wherein the treatment method is selected from the group consisting of a polyethylene resin and a fluororesin. 3. The method according to claim 1, wherein the gas is one or a mixture of two or more selected from the group consisting of oxygen, nitrogen, helium, argon and other noble gases. 4. The method according to claim 1, wherein the gas is blown onto the surface of the plastic. 5. A gas flow rate of 0.05 to 40 L / min · c from a blow port provided at a blow angle (α) of 0 to 90 degrees and a blow distance (d) of 1 to 40 cm with respect to the plastic surface.
blown attached claim 4 processing method described in m ^2. 6. The processing method according to claim 1, wherein the plastic has a three-dimensional shape.