JPH04328135A - Corona discharge treatment of resin molded product and system therefor - Google Patents

Abstract

PURPOSE:To provide uniform, favorable corona discharge treatment on the entire resin molded product by applying a high-voltage pulse of specified waveform between a discharge electrode and counter electrode set up with a resin molded product put in between to generate corona discharge, with spark discharge hard to occur. CONSTITUTION:A resin molded product 10 such as an automotive instrument panel pad with three-dimensional design is put between a discharge electrode 30 and its counter electrode 20, and a high-voltage pulse 10-100KV in wave height value, <=1muS in pulse width and 10-1000pps in pulse frequency is applied between them to generate corona discharge, thus providing favorable corona discharge treatment on the entire surface of the product including the edge proximities.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a corona discharge treatment method and apparatus for resin molded products, and more specifically, corona discharge treatment is carried out to improve paintability, printability, adhesion, etc. to the surface of resin molded products. The present invention relates to a method of corona discharge treatment and a corona discharge treatment apparatus used in this method.

0002

BACKGROUND OF THE INVENTION It is well known that by subjecting the surface of a resin film made of polypropylene or the like to corona discharge treatment, the printability and adhesion of the film surface can be improved, and this is used in the manufacture of various products. Corona discharge treatment is performed under normal pressure not only on resin films but also on the surfaces of resin molded products with three-dimensional shapes.
Efforts are being made to improve paintability, adhesion, etc.

Corona discharge treatment uses a pair of electrodes, a discharge electrode and a counter electrode, and the object to be treated is placed between the pair of electrodes, and a high voltage is applied between the electrodes under normal pressure to generate corona discharge. By generating corona discharge, the surface of the object to be treated is subjected to corona discharge treatment. At this time, an AC high frequency voltage is usually used as the high voltage applied between the electrodes. AC high frequency voltage is said to easily cause corona discharge and is excellent in surface treatment effects. In addition, JP-A-47-48
No. 90 discloses that corona discharge treatment for a film is carried out.
A technique using a voltage pulse with a pulse width of about 100 to 200 microseconds has been disclosed, and it is said that the use of such a voltage pulse improves the processing effect.

[0004] When performing corona discharge treatment on a three-dimensional resin molded product, the three-dimensional resin molded product is thicker than a resin film, and the thickness may be partially different or the outer shape may be different. There is a problem in that it is difficult to uniformly apply corona discharge treatment to the entire surface because the surface is uneven and has through holes. As a conventional corona discharge treatment method for a three-dimensional resin molded article, there is a method disclosed in Japanese Patent Application Laid-Open No. 119931/1983. This method uses a pair of electrodes, a holding electrode and a counter electrode, to hold the object to be processed on the holding electrode, and to ensure that the tip of the flexible discharge device attached to the counter electrode is always in the position of the object to be processed. An AC high-frequency voltage is applied between the holding electrode and the counter electrode while moving the holding electrode and the object to be processed, the counter electrode, and the flexible discharge device relative to each other at a constant distance from the surface of the object. to generate corona discharge.

Furthermore, in the method disclosed in Japanese Patent Application Laid-Open No. 62-57431, a discharge electrode having a curved discharge tip is moved at a frequency of 20 to 30 kHz while relatively moving along the shape of the object to be treated. AC high frequency output is applied to generate corona discharge.

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional corona discharge treatment method for a three-dimensional resin molded product, the edges existing on the outer periphery of the resin molded product, the inner periphery of the opening, etc. , there was a problem that sufficient processing could not be performed. This is because in the conventional method, when the discharge electrode approaches the edge of the resin molded product, the distance between the discharge electrode and the counter electrode, the so-called interpolar distance, becomes smaller, which stabilizes corona discharge, which is effective for surface treatment. This is because the corona discharge treatment cannot be sufficiently performed near the edges because spark discharge occurs due to dielectric breakdown. Under conventional conventional treatment conditions, it is often not possible to perform sufficient corona discharge treatment on a range of about 20 mm from the edge of a resin molded article.

Spark discharge is likely to occur near the edges of resin molded products due to dielectric breakdown, because if there is a resin molded product between the discharge electrode and the counter electrode, there is less possibility of dielectric breakdown occurring. However, near the edges mentioned above, a short circuit occurs between the two electrodes directly through the air, generating a spark discharge, and current flows easily along the surface of the resin molded product, resulting in dielectric breakdown. That's what happens.

In order to avoid the occurrence of spark discharge, it is necessary to keep the discharge electrode and the counter electrode close to the edge of the resin molded product, but if this is done, corona discharge will not reach near the edge,
Not enough processing is done. Furthermore, if the voltage applied between the discharge electrode and the counter electrode is reduced, spark discharge due to dielectric breakdown becomes less likely to occur, and the electrode can be brought closer to the edge of the resin molded product, but of course, if the voltage is small, The surface treatment effect due to corona discharge is also weakened, and the treatment effect of the entire resin molded product is reduced.

[0009] In the above-mentioned Japanese Patent Application Laid-open No. 62-57431,
A technique has been disclosed in which a buffer plate made of a dielectric material such as epoxy resin is fitted into the opening of a resin molded product to prevent corona discharge from being disturbed in the opening. However, with this method, a buffer plate with a shape that matches the hole in the resin molded product is prepared, and the buffer plate is attached to each hole, or the buffer plate is attached to the counter electrode. This method is time-consuming and has the drawback of significantly reducing work efficiency and electrode production efficiency. Furthermore, if there is even a slight gap between the opening and the buffer plate, there is a possibility that dielectric breakdown may occur through this gap and spark discharge will occur, resulting in poor reliability.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a corona discharge treatment method for a resin molded article that can perform a good corona discharge treatment on the entire surface of a resin molded article having a three-dimensional shape, including near the edges. There is a particular thing. Another object of the present invention is to provide a corona discharge treatment apparatus used to suitably carry out the above method.

[0011]

[Means for Solving the Problems] The inventors conducted experiments by variously changing the waveform of the high voltage applied to the discharge electrode, and found that even if other conditions were the same, sparks were generated under normal pressure due to the difference in the waveform. It has been found that there are waveform conditions in which the voltage for starting discharge is different and corona discharge is effective for surface treatment. As a result of studying waveform conditions that are less likely to cause spark discharge and are effective for surface treatment, the present invention was completed.

[0012] In the corona discharge treatment method for resin molded articles according to the present invention, which solves the above problems, a resin molded article having a three-dimensional shape is placed between a discharge electrode and a counter electrode, and a high voltage is applied between the two electrodes. In this method, a corona discharge treatment is applied to the surface of a resin molded product by applying a corona discharge to generate a corona discharge.
Hereinafter, the method is characterized in that corona discharge is generated by high voltage pulses with a pulse frequency of 10 to 1000 pps.

[0013] Furthermore, the corona discharge treatment apparatus for resin molded products according to the present invention generates corona discharge by applying a high voltage between a discharge electrode and a counter electrode arranged opposite to each other, and a high voltage between the discharge electrode and the counter electrode. In a corona discharge treatment apparatus that performs corona discharge treatment on the surface of a resin molded product having a three-dimensional shape, the high voltage power source is equipped with a power supply section that generates high voltage direct current and a high voltage direct current that is connected to the high voltage direct current. Equipped with a pulse forming part that converts into voltage pulses, the peak value is 10~
100kV, pulse width 1μs or less, pulse frequency 10
It is characterized by being a high voltage pulse power source that generates high voltage pulses of ~1000 pps.

[0014] The resin molded article may be made of any resin whose surface characteristics can be improved by corona discharge treatment, such as polypropylene, polyethylene, or other polyolefin resins. Since the polyolefin resin does not have a polar group, it has a problem of poor adhesiveness and printability, and corona discharge treatment is effective in improving these properties. It goes without saying that the material for the resin molded product may contain various additives such as rubber materials, pigments, fillers, antioxidants, and ultraviolet light inhibitors, as necessary, in addition to the above-mentioned resins.

[0015] The resin molded product may have any three-dimensional shape, such as uneven parts, ribs, or openings, depending on the purpose of use of the resin molded product. This invention is
A good treatment effect can be exerted on resin molded products in which openings are formed in some parts. Specific examples of resin molded products include automobile instrument panel pads (so-called instrument panel pads), bumpers, moldings, and the like.

The structure of the discharge electrode and the counter electrode may be the same as that of a corona discharge treatment apparatus for ordinary resin molded products, and any known electrode structure can be freely employed. Specifically, for example, as the counter electrode, one is used that has a three-dimensional shape corresponding to the inner surface shape of the resin molded product and can be inserted into the inner surface of the resin molded product to hold the resin molded product. . Although it is desirable that the counter electrode and the resin molded product are in close contact with each other over the entire surface, it is not a big problem even if there are some parts that are separated from each other. When the counter electrode and the resin molded product are partially separated, corona discharge treatment can be sufficiently performed if the distance is about 10 mm or less. As for the structure of the counter electrode, the entire structure may be made of a conductive material, or, for example, a thin flexible conductive material may be used on the surface of the base material made of an insulating material such as FRP. For example, it may have a structure in which copper foil or aluminum tape is pasted.

As the discharge electrode, a discharge electrode of a known shape generally used in corona discharge treatment can be used. For example, a three-dimensional shape of a resin molded product is cut into a plurality of cross sections, and for each cut cross section, A large number of thin plate-shaped electrodes with cut edges corresponding to the cross-sectional shape or knife-edge shaped electrodes are arranged at each cross-sectional position of the resin molded product at a fixed distance from the surface of the resin molded product. The one placed is used. Further, a large number of needle-like electrodes or brush-like electrodes arranged at a certain distance from the surface of the resin molded product may also be used. Alternatively, a large number of needle-like or brush-like electrodes attached to the thin plate-like or knife-edge-like electrode tips may be arranged at a certain distance from the surface of the resin molded product in the same manner as above. .

[0018] The distance between the discharge electrode and the surface of the resin molded product is preferably constant as a whole, and although the distance varies depending on conditions such as the shape of the electrode and the applied voltage, it is usually 5 to 5. It is preferable to set it in a range of about 50 mm, more preferably in a range of 10 to 20 mm. In addition, it is preferable that the variation in the distance depending on the location of the resin molded product be as small as possible;
If the variation is about 0 mm or less, it will not have much effect.

[0019] The discharge electrode may be moved relative to the surface of the resin molded product to treat the entire resin molded product. For this relative movement, the resin molded product must be fixed.
The discharge electrode moves horizontally, the discharge electrode moves horizontally and also moves vertically, or the discharge electrode is fixed and the resin molded product and counter electrode move. In some cases, both the resin molded product and the counter electrode move. However, from the viewpoint of safety as an electrical equipment, it is more preferable that the discharge electrode side to which a high voltage is applied is fixed. The means of transportation are
It is possible to employ moving means in ordinary mechanical devices, such as a conveyor mechanism or a cylinder mechanism.

[0020]If the discharge electrode and the resin molded product are relatively oscillated in the horizontal or vertical direction at a constant period, it is effective to apply a uniform corona discharge treatment to the entire surface of the resin molded product. It is. Specific rocking conditions include, for example, a rocking stroke of 3 to 60 mm, and a rocking speed of 40 to 60 mm.
It can be set to about 400 mm/min. The specific rocking stroke and rocking speed can be changed as appropriate depending on the geometric shapes of the resin molded product and the discharge electrode. Although it is preferable for the swinging direction to be in multiple directions, such as front, back, left, and right, a sufficient processing effect can be obtained by swinging only in one direction, such as the longitudinal direction of the resin molded product. As the means for causing the rocking, an eccentric cam mechanism, a crank mechanism, or other rocking means in a normal mechanical device can be employed.

[0021] The resin molded product can be easily placed if it is placed at a processing position between the discharge electrode and the counter electrode using a suitable conveyance means, that is, a moving means. The moving means can be composed of various conveyor mechanisms, lift mechanisms, and the like. If the moving means moves the resin molded product together with the counter electrode, the resin molded product can be easily handled.

[0022] The discharge electrode and the counter electrode are connected to a high voltage pulse power source. A high-voltage pulse power source is a device that generates high-voltage pulses having a specific waveform, which will be described later, from commercial alternating current or direct current, and incorporates a pulse shaping circuit that converts such waveforms. The high voltage pulse power supply has a peak value of 10 to 100 kV and a pulse width of 1 μs.
Hereinafter, the specific circuit structure can be arbitrarily set as long as high voltage pulses with a pulse frequency of 10 to 1000 pps can be generated. Specifically, various circuit structures or devices conventionally used as impulse high voltage generators may be used. To generate high-voltage pulses with the waveforms described above, a power supply unit that generates high-voltage DC from a normal commercial AC power supply or DC power supply, and a high-voltage DC power supply that converts this high-voltage DC into high-voltage pulses are required. It is preferable to use a device consisting of a pulse forming section that performs conversion.

The waveforms of high voltage pulses are schematically shown in FIGS. 2 to 4, and will be explained below with reference to these figures. The waveform of the high voltage pulse changes depending on the circuit constants, and in a normal impulse high voltage generation circuit, the waveform is unidirectional,
It is known to exhibit critical braking waveforms, damped vibration waveforms, etc. FIG. 3 schematically shows the critical braking waveform, and FIG. 4 schematically shows the damped vibration waveform. In this invention, any of the unidirectional waveform, critical damping waveform, and damped oscillation waveform may be used. However, in the case of a damped oscillation waveform, the conditions such as the pulse width described above are applied to the first wave. It shall be.

Pulse waveforms include positive polarity pulses, negative polarity pulses, and alternating pulses in which both waveforms appear alternately, and any of these pulses can be used in the present invention. However, in the case of alternating pulses, it is technically difficult to generate high voltage pulses with narrow pulse widths such as those used in this invention, and there are problems with withstand voltage, so it is difficult to use in power supply circuits. It is difficult to manufacture and the equipment cost is high. Therefore, a high voltage pulse with a narrow pulse width can be easily created using a positive polarity pulse or a negative polarity pulse.
The circuit configuration is simple and economical, which is preferable. In addition, when corona discharge treatment is performed on a film, it is desirable to use a symmetrical voltage waveform in order to make it easier to wind up the film after treatment, but with three-dimensional shaped resin molded products, winding is not necessary. , there is no problem even if the waveform is not symmetrical.

FIG. 2 shows an enlarged view of the main part of the waveform. The peak value is defined by the height H of the waveform W from 0 to the peak while the voltage rises and falls. However, in FIG. 2, the scale on the vertical axis is shown as a percentage with the voltage at the peak being 100%, so H does not directly indicate the voltage value. The higher the peak value of the high voltage pulse, the more likely corona discharge will occur and the higher the treatment effect will be. Furthermore, if the same level of processing is sufficient, the distance between the electrodes can be increased. Wave height is 10k
If it is less than V, corona discharge, which is effective for surface treatment of resin molded products, is difficult to occur. When the peak value exceeds 100 kV, there is not much improvement in the treatment effect, but it is difficult to handle high voltages, legal regulations such as electrical equipment technical standards become stricter, and the voltage-resistant structure of the equipment becomes more extensive. , it is not practical because the manufacturing cost of the device is high. The preferred range of the peak value is 40 to 80 kV.

The pulse width is defined by a value called wave tail in the definition of the impulse voltage waveform. Wave tail length is simply the time T required for the voltage value to drop to 1/2 of the maximum value after it rises from a state of 0.
It is expressed as 2'. More precisely, in the waveform of the high voltage pulse shown in FIG.
1 and point X2 of 90% voltage intersects the line of 0% voltage, time T2 until the voltage drops to 50% of the peak value H is the wave length. Defined. However, in actual measurement, the waveform W
Even if the time T2' from the origin 0 to the point where the voltage drops to 50% of the peak value H is measured, it is not much different from T2. Therefore, in practice, there is no problem even if the pulse width is defined by T2' instead of T2.

[0027] The narrower the pulse width, the less likely spark discharge will occur, and the effects of the present invention can be better exhibited. When the pulse width exceeds 1 μs, the pulse waveform rises slowly, making it impossible to accelerate only the electrons effectively.
The acceleration of ions increases, leading to a rise in gas temperature,
As a result, spark discharge is likely to occur. In addition, active species such as oxygen radicals and atomic oxygen, which are effective in surface treatment, are generated by the action of high-speed electrons, so if the electrons cannot be effectively accelerated, the treatment effect will be reduced. If the pulse width is less than 100 ns, it becomes difficult to manufacture a pulse waveform generating circuit, so in practice, the pulse width is 100 ns or more in order to be applied to a production site. The preferred range of pulse width is 100 to 700
It is ns.

[0028] The higher the pulse frequency, the better the processing efficiency. If the pulse frequency is less than 10 pps, the processing takes a long time and is not practical. When the pulse frequency exceeds 1000 pps, it is difficult to generate such a problem using a normal high voltage pulse power supply. However, if a thyratron or the like is used as a high voltage switch, it is possible to achieve a pulse frequency of 1000 pps or more, but the device becomes expensive. When adopting a switching system using a ball gap or rotary spark gap, which is technically simpler than the thyratron, for the pulse forming part of a high-voltage pulse power supply, the pulse frequency is usually about 50 to 400 pps. . Therefore, in practice, the preferred value of the pulse frequency is about 100 to 200
It will be about pps.

The pulse waveform has the so-called wavefront length (w
By shortening the ave front), the rise of the waveform can be made faster. As a result, as mentioned above, electrons can be accelerated well, spark discharge can be prevented, and
Moreover, the processing effect can be improved. Therefore, even if the pulse width is the same, it is preferable that the wavefront length is shorter. In addition, in the definition of impulse voltage waveform, the wavefront length is
In FIG. 2, the time interval T1 is defined as the time interval T1 between the point X3 and the point X0, where the extension of the line connecting the points X1 and X2 intersects the 100% voltage line.

Each step of the corona discharge treatment is carried out in the same manner as in a normal corona discharge treatment under normal pressure, except that a high voltage pulse having the waveform described above is used. For example, if the surface of a resin molded product is dirty, cleaning the surface in pretreatment will improve the treatment effect. When performing corona discharge treatment, the treatment effect will be improved if the surface of the resin molded product is heated in a temperature range of 40° C. or higher and below the softening point of the resin molded product.

As mentioned above, when processing a large number of thin or knife-edge discharge electrode plates arranged along the cross-sectional shape of a resin molded product, a high voltage pulse is supplied to all the discharge electrode plates at the same time. Instead of causing the corona discharge by using the discharge electrode plates, a high voltage pulse may be alternately supplied to one of the adjacent discharge electrode plates to cause the corona discharge. In this case, it is possible to eliminate an insufficiently treated portion that occurs on the surface of the resin molded product immediately below the intermediate position between adjacent discharge electrode plates.

[0032]

[Operation] The high voltage pulse having the waveform as described above is
Compared to conventional high-frequency AC, the voltage required to initiate spark discharge is higher. This may be due to the following reasons. When a high voltage is applied between a pair of electrodes, an electron avalanche first extends from the cathode side to the anode side, and when the electron avalanche reaches the anode, an ion streamer then extends from the anode side to the cathode side. When this ion streamer reaches the cathode, the insulation between the electrodes is completely destroyed and spark discharge begins. Therefore, if the voltage application is ended before such spark discharge starts, that is, before the ion streamer reaches the cathode and complete circuit breakdown occurs, spark discharge will not occur.

[0033] When a high voltage pulse with a narrow pulse width is applied between the electrodes, the voltage rises rapidly, then falls rapidly and disappears. Due to the sudden increase in voltage, the aforementioned electron avalanche grows rapidly and corona discharge occurs, but ions, which have a much slower speed than electrons, move between the electrodes and fill the entire space between the electrodes. Since it takes time for path breakdown to occur, the voltage will disappear before spark discharge starts. That is, although corona discharge occurs well, spark discharge is difficult to occur.

Furthermore, since the treatment effect of corona discharge is greatly influenced by active species such as oxygen radicals and atomic oxygen generated by the electron avalanche, a high voltage pulse with a rapid increase in voltage is In comparison, the efficiency of corona discharge treatment is improved. Furthermore, a high voltage pulse in which the voltage rises rapidly can process a wider area than an AC high frequency because the tip of the corona discharge can easily extend.

Therefore, if a corona discharge is generated by a high voltage pulse with a narrow pulse width, the electrode can be brought close to the outer periphery of a resin molded product having a three-dimensional shape or near the edge existing on the inner periphery of an opening. There is no need to worry about spark discharge. As a result, it becomes possible to perform good corona discharge treatment even near the edges, and uniform and good corona discharge treatment can be performed on the entire surface of the resin molded product having a three-dimensional shape.

[0036] Furthermore, in the conventional method of generating corona discharge using AC high frequency, the frequency is usually set at 5 to 30 kHz.
This means that positive and negative voltages are applied at a frequency of approximately 5000 times/second or more, and assuming that corona discharge occurs near the maximum voltage of each positive and negative voltage, this can be converted into a pulse frequency. In other words, it is 10,000 pps or more. As described above, the higher the pulse frequency, the higher the processing effect, but it is technically extremely difficult to generate high voltage pulses at a pulse frequency of 5000 pps or more. However, if a high voltage pulse with a narrow pulse width is used as in this invention, the processing capacity per pulse is extremely high. It is possible to achieve a processing effect equal to or greater than that of high frequency.

When performing corona discharge treatment using a single-polarity high voltage pulse, the uniformity of the treatment can be improved by relatively oscillating the discharge electrode and the counter electrode, that is, the resin molded product. This is because if discharge treatment is performed with the discharge electrode stationary relative to the resin molded product, the space charges formed by the tips of adjacent discharge electrodes may repel each other, and residual charges remaining on the surface of the resin molded product may This is because the discharge treatment on the surface of the resin molded article may become insufficient immediately below the intermediate position between the tips of both discharge electrodes due to mutual repulsion. In the above-mentioned conventional corona discharge treatment using AC high frequency, the voltage is alternately switched between positive and negative, so space charges and residual charges on the resin surface are easily canceled out. However, with single polarity pulses, space charges are formed and residual charges are Charges may remain on the resin surface. Therefore, if the discharge electrode and the resin molded product are swung relative to each other, the intermediate positions of the tips of the adjacent discharge electrodes will also be swung, which eliminates the insufficiently processed areas due to the space charge and residual charge. Uniform discharge treatment can be performed on the entire surface of the resin molded product, including the area directly below the intermediate position between the discharge electrodes.

[0038]

Embodiments Next, embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic structure and basic circuit configuration of a corona discharge treatment apparatus according to the present invention. As the resin molded product 10, an automobile bumper mainly made of polypropylene is used. An opening 12 is formed in a part of the resin molded product 10 for attachment to a vehicle body or other parts.

The counter electrode 20 has an outer shape corresponding to the inner shape of the resin molded product 10, and is made by pasting a conductive material such as copper foil or aluminum tape on a base material made of a resin material such as FRP. It is formed by The resin molded product 10 is fitted and held by this counter electrode 20. The counter electrode 20 may be made of a material as long as a conductive material is present on at least the surface thereof, and in addition to the above structure, for example, the base material may be coated with a conductive paint. The material of the base material is also the FR
In addition to P, insulating materials such as epoxy resin, acrylic resin, and vinyl chloride resin can be used. The counter electrode 20 is supported by a support member 22, and the support member 22 is movable in the horizontal and vertical directions. A moving mechanism for the support member 22 is not shown.

A discharge electrode 30 is placed above the resin molded product 10.
is located. The discharge electrode 30 is arranged to face the surface of the resin molded product 10 at a certain distance. A high voltage pulse power source 40 is connected to the counter electrode 20 and the discharge electrode 30 via wiring. The high-voltage pulse power source 40 includes a power supply section 50 that obtains high-voltage direct current from a general-purpose alternating current power source, and a pulse forming section 60 that converts the high-voltage direct current supplied from the power supply section 50 into high-voltage pulses. The power supply section 50 includes a booster circuit or a transformer circuit in a normal power supply device. Power supply section 50
The voltage of the high voltage direct current supplied from the source may be about 50 to 150 kV, preferably set to about 70 to 120 kV. The pulse forming section 60 includes a ball gap type pulse forming circuit.

The circuits of the illustrated power supply section 50 and pulse forming section 60 will be briefly explained. Power supply section 50
has a charging resistor 52 (resistance value: about 1 to 10 MΩ, preferably about 2 MΩ), and the pulse forming section 60 has a charging/discharging capacitor 64 (capacitance: about 1 to 4 nF, preferably 2 to 3 nF). , ball gap mechanism 62, discharge resistance 66 (resistance value: 25-300Ω, preferably 50-10Ω)
0Ω), etc. The power supply unit 50 obtains high-voltage direct current from commercial power AC (three-phase 220 V, 50/60 Hz) through a transformer circuit and a rectifier circuit. The ball gap mechanism 62 has a diameter of 120 mm, for example.
The balls are opposed to each other with a distance of about 5 to 40 mm, and a switching operation is performed by causing a discharge between the opposing balls. By adjusting the interval between opposing spheres, the so-called sphere gap gap, the discharge starting voltage Vs at the sphere gap changes, and as a result, the peak value of the high voltage pulse applied to the discharge load system 90 can also be changed. By supplying dry air around the ball gap mechanism 62, the switching operation can be performed favorably. The function of converting commercial alternating current into pulses in such a circuit is well known in the art, and detailed explanation will be omitted.

In the high voltage pulse power supply 40 having the circuit configuration as described above, the peak value and pulse width of the high voltage pulse obtained by the pulse forming section 60 are determined by the ball gap mechanism 62, the charging/discharging capacitor 64, and the discharging resistor. In addition to the characteristics of each circuit element such as 66, the discharge electrode 30 - resin molded product 10 -
It is affected by the capacitance and resistance of the discharge load system 90 consisting of the counter electrode 20, or the stray capacitance and stray reactance of the entire discharge circuit including the discharge load system 90. Furthermore, since the corona discharge phenomenon itself is a dynamic phenomenon and exhibits nonlinear behavior, it is difficult to accurately describe it using transient phenomenology based on linear circuit theory. For example, the pulse width is affected by the capacitance of the charging/discharging capacitor 64 and the resistance value of the discharging resistor 66, and the pulse height value is influenced by the ball gap discharge starting voltage VS, the capacitance of the charging/discharging capacitor 64, and the discharge load system. For example, it is affected by capacitance. Therefore, in order to obtain a desired pulse waveform with the high-voltage pulse power source 40, the characteristics of each circuit element and the combination thereof are determined by the structure and material of the resin molded product 10 to be subjected to corona discharge treatment, the discharge electrode 30, and the counter electrode 20. You need to choose appropriately.

With the illustrated high voltage pulse power supply 40, the discharge voltage in the discharge load system 90, that is, the peak value is 40 to 60 kV,
A pulse with a pulse width of about 200 to 500 ns is obtained, and this pulse can be applied between the discharge electrode 30 and the counter electrode 20 at a pulse frequency of about 40 to 100 pps to generate corona discharge. If the resin molded product 10 is treated for about 20 to 120 seconds, a good surface treatment can be achieved. Specifically, when the surface of the resin molded product 10 is coated, the coating peel strength is 1.0 kg/cm.
It has been confirmed that this will be the case.

However, the illustrated circuit configurations of the power supply section 50 and the pulse forming section 60 are for explaining the basic functions, and if similar functions can be realized, such circuits are not necessarily required. There isn't. 5 and 7 show specific structures of the discharge electrode 30 and the counter electrode 20.

A plurality of insulating electrode support plates 33 made of epoxy resin, acrylic resin, vinyl chloride resin, etc. are fixedly attached to two parallel power supply lines 31 and 32 at regular intervals. The installation interval of the electrode support plates 33 is usually 20~
It is sufficient to set it to about 40 mm. A conductive discharge electrode plate 34 is provided on one side of the electrode support plate 33, and the discharge electrode plate 34 is electrically connected to the power supply lines 31 and 32 via terminals 35. The discharge electrode plates 34 of adjacent electrode support plates 33 are alternately connected to left and right power supply lines 31 and 32. The edges of the discharge electrode plate 34 are aligned with the cross-sectional shape of the resin molded product 10 facing each other at each position.
It is cut out in a concave shape, and the distance between the discharge electrode plate 34 and the surface of the resin molded product 10 is approximately constant at any position. The distance between the discharge electrode plate 34 and the resin molded product 10 may be set to about 10 to 30 mm.

The structure of the discharge electrode 30 is shown in FIG.
As shown in the figure, needle-shaped or brush-shaped discharge electrodes 39 are attached to the discharge electrode plate 34 at intervals of about 20 mm, so that the distance between the tips of the brush-shaped discharge electrodes 39 and the surface of the resin molded product 10 is constant. It may have a structure like this. The counter electrode 20 is
It is provided so as to fit snugly into the inner shape of the resin molded product 10.

By adopting the above electrode structure, it is possible to prevent an insufficiently processed portion from remaining directly under the intermediate position of the plurality of discharge electrode plates 34 due to space charges or residual charges on the surface of the resin molded product. As schematically shown in FIG. 8, at an intermediate position between adjacent discharge electrode plates 34, discharge electrode plates 3 on both sides
Since the space charges formed by 4 and 34 and the residual charges on the resin molded product repel each other, there is a possibility that an insufficiently processed portion d with a width of approximately 1 to 2 mm may occur. Discharge electrode plate 34
, 34, the greater the repulsion of space charges and residual charges. Therefore, when the discharge electrode plates 34, 34 are brought closer together, the insufficiently processed portion d becomes even more noticeable.

Therefore, as shown in FIG. 9, among the discharge electrode plates 34 connected to the two power supply lines 31 and 32, a high voltage pulse is applied only to the discharge electrode plate 34a connected to one of the power supply lines 31. Apply and discharge. That is, among the plurality of discharge electrode plates 34, every other discharge electrode 34a
will be discharged. Then, as described above, an insufficiently processed portion e remains at the intermediate position between the discharge electrode plates 34a and 34a. However, in this case, since the distance between the discharge electrode plates 34a and 34a is wide, the repulsion of space charges and residual charges is not so strong, and the treatment is weaker in the insufficiently treated area e than in other areas. This insufficiently processed portion e is located directly below the discharge electrode plate 34b connected to the other power supply line 32.

Thereafter, as shown by the dashed line in FIG. 9, a high voltage pulse is not applied to the power supply line 31, but a high voltage pulse is applied only to the other power supply line 32, so that the discharge electrode that was not discharged last time is If only the plate 34b is discharged, sufficient treatment will be applied to the insufficiently treated portion e in the previous stage, which is directly under the discharge electrode plate 34b. In this way, no insufficiently treated portion e remains between the discharge electrode plates 34, 34, and uniform corona discharge treatment can be performed on the entire resin molded product 10. If this method is adopted, uniform processing can be performed without shaking the discharge electrode 30, the counter electrode 20, and the resin molded product 10. This method can also be combined with rocking.

The power supply lines 31 and 32 are energized at the same time, and the opposing electrode 20 side, that is, the resin molded product 10, is connected to the discharge electrode 30.
It goes without saying that uniform processing can be achieved by oscillating the device relative to the object. Further, when processing is performed by performing swinging, it is not necessary to have two power supply lines, and there is no problem even if there is only one power supply line. Furthermore, while performing rocking,
When power is supplied simultaneously by the two power supply lines 31 and 32, or when power is supplied by one power supply line, the electrode support plate 33 does not need to be made of an insulating material,
It may be made of the same conductive material as the discharge electrode plate 34. In this case, the electrode support plate 33 and the discharge electrode plate 3
4 can be integrated to form the discharge electrode 30, which simplifies the structure.

A more specific example will be explained below. - Example 1 - First, the performance of the corona discharge treatment method using high voltage pulses of the present invention and the conventional corona discharge treatment method using AC high frequency was compared. The results were as follows.

As shown in FIG. 10, a resin molded product 10 is placed between the counter electrode 20 and the discharge electrode 30, and the discharge electrode 30 is
A high voltage is applied between the electrode 20 and the counter electrode 20 to generate corona discharge, and the resin molded product 10 is subjected to corona discharge treatment. At this time, the distance from the tip of the discharge electrode 30 to the resin molded product 10 is set so that the discharge electrode 30 and the counter electrode 20 can be closest to each other in a state where good corona discharge treatment can be performed without causing spark discharge.
The distance h to the counter electrode 20 was measured along the surface of . The measurements were repeated by changing the applied voltage.

FIG. 11 shows the measurement results. Under the same applied voltage conditions, compared to the comparative example using AC high frequency,
In the embodiment of the present invention using pulses, the distance of closest approach h was much shorter, and it was demonstrated that good corona discharge treatment could be performed up to a position close to the edge of the resin molded product 10. In addition, in the comparative example using AC high frequency, it was difficult to increase the applied voltage above 30 kV due to the performance of the power supply, but in the example of this invention using pulses, the applied voltage could be easily increased to nearly 60 kV. I was able to raise it. Therefore, it was confirmed that by using high voltage pulses, the treatment effect can be enhanced and corona discharge treatment can be performed more efficiently.

- Example 2 - Using the apparatus shown in FIG.
Using the method of this invention, a polypropylene automobile bumper was subjected to corona discharge treatment as follows. <Test material> Polypropylene front bumper for automobiles Degreased and cleaned under the following conditions before corona discharge treatment <Degreasing conditions> Treatment agent: Surf Cleaner 53SR (manufactured by Nippon Paint Co., Ltd., water-based cleaning agent for resins) Treatment Conditions: 60-65℃ x 2 minutes, spray pressure 1kg/
cm2 Hot water wash at 40℃ x 2 minutes, forced drying at 80-90℃ x 20
About 1 minute <Corona discharge treatment conditions> Temperature and humidity: 19°C, 76% Applied voltage: Ball gap discharge starting voltage Vs = 80 kV, DC set voltage Vin = 120 kV, (Vin: DC of the power supply unit displayed on the control panel High voltage value) Pulse peak value: H = 54 kV Pulse width: T2' = 400 ns Pulse frequency: 100 pps Discharge time: 30 seconds at the above DC setting voltage Discharge oscillation: The bumper was reciprocated with a stroke of 4 mm in the longitudinal direction.

[0055] Swinging speed: 80 mm/min Discharge electrode: Structure shown in Figs. 5 to 7. A large number of brush-like discharge electrodes 39 were planted on the edge of a discharge electrode plate 34 made of brass. The pitch of the discharge electrode plates 34 was 20 mm. Power was supplied to both power supply lines 31 and 32 at the same time. Counter electrode: Fabricated by covering a main body made of FRP with copper foil, aluminum tape, and Teflon (trademark of DuPont) tape.

Distance between brush-shaped discharge electrode 39 and bumper surface: Approximately 10 mm Charge/discharge capacitor capacity: 2.4 nF Charge resistance: 6 MΩ Discharge resistance: 25Ω Ball gap interval: 35 mm Dry air supply pressure 0
．． 5kgf/cm Primary side input current: 10.0A (3-phase 220V) Bumper temperature: Discharge treatment performed at room temperature (19℃) When corona discharge treatment was performed under the above treatment conditions, good corona discharge occurred. However, no spark discharge was observed.

Three bumpers were subjected to corona discharge treatment under the above treatment conditions, and each was painted. <Painting/baking conditions> Painting period: The surface-treated bumpers were left for a certain period of time, and painted immediately, 24 hours later, or one week later.

[0058] Leaving temperature and humidity: No particular control, 10-25°C
It was 50-80%. Paint: R-271 White (manufactured by NBC) Tensilon evaluation film thickness: 100 to 200 μm (no special primer used) Baking drying: 90°C x 40 minutes In this way, after baking the paint, leave it indoors for 24 hours After that, a Tensilon peel test was conducted, and the results shown in the table below were obtained.

[0059]

[Table 1]

In the table, [No peeling] indicates that the coating film did not peel off from the bumper and tensilon measurement could not be performed. Measurement points A to D were set at multiple locations including the flat part and end of the bumper, the edge of the opening, and the like. In addition, for areas where the Tensilon peel test was not possible due to the shape, a cross-cut 1 mm width cellophane tape cross-cut peel test was conducted, and it was confirmed that no peeling occurred even in this test.

From the above test results, the corona discharge treatment method according to the present invention can be used without generating spark discharge.
It was confirmed that uniform and good corona discharge treatment could be performed on the entire resin molded article including the edges. It was also confirmed that the effect of improving coating film adhesion by the discharge treatment was maintained even after one week had passed after the discharge treatment. - Example 3 - In this example, differences in processing effects based on differences in the structure and operation of the discharge electrode 30 were compared. However, since the swinging distance was long, the discharge electrode for only the central part was used for processing one bumper, and the discharge electrodes for both sides were removed.

Using the discharge electrode 30 shown in FIGS. 5 to 7, the electrode plate of this discharge electrode was subjected to discharge treatment under the following usage conditions. (I) In FIG. 9, only the discharge electrode plate 34a was used. (II) In FIG. 9, only the discharge electrode plate 34a is used, and the entire counter electrode 20 is horizontally spaced by 50 mm.
Shake it. (Rocking speed: 300 mm/min) (III) As shown in FIG. 8, the discharge electrode plates 34a, 34
b was used at the same time.

(IV) As shown in FIG. 8, the discharge electrode plates 34a and 34b are used simultaneously, and the counter electrode 20
The whole was swung horizontally by 50 mm. (oscillation speed 30
0 mm/min) (V) In FIG. 9, the discharge electrode plates 34a and 34b were switched and discharged alternately. The discharge time is expressed as the sum of the discharge times of the discharge electrode plates 34a and 34b.

Note that the tip of the discharge electrode 30 and the resin molded product 1
The distance to the 0 surface was 10 mm. The mounting pitch of the discharge electrode plates 34 was 16 mm. Therefore, the pitch interval when only one set of discharge electrode plates 34a or 34b is discharged is 32 mm. Ball gap discharge starting voltage V
s was 70 kV, and the DC set voltage Vin was 80 kV. The treatment time was 15, 30, and 60 seconds.

After coating the treated resin molded article 10, the peel strength of the coating film was measured. FIG. 12 shows the test results. Comparing (I) and (II) or (III) and (IV) in this test result, it can be seen that the processing effect is improved by swinging the counter electrode 20. In (III), the downwardly protruding portion of the graph indicates that locally low processing remains. Comparing (III) and (V), it can be seen that by switching the discharge electrode plates 34a and 34b and discharging alternately, it is possible to eliminate localized areas where the treatment is insufficient and to achieve uniform treatment. I understand.

- Example 4 - In this example, the effect of heating the resin molded product 10 was confirmed. Corona discharge treatment was performed under substantially the same treatment conditions as in Example 2. However, the ball gap discharge starting voltage Vs was 70 kV, and the DC set voltage Vin was 80 kV. In addition, before performing the corona discharge treatment, the resin molded product 10 is heated to 40 to 50°C.
The temperature was raised to . At the stage where the corona discharge treatment was completed, the temperature of the resin molded article 10 was 25 to 35°C. For comparison, the same corona discharge treatment was also performed on the resin molded product 10 at room temperature (14 to 24° C.) without heating. At the same time, various treatments were performed while changing the surface material of the counter electrode 20. The resin molded article 10 that had undergone the discharge treatment was coated with the paint and baking conditions shown in Example 2, and 24 hours later, a Tensilon peel test was conducted.

FIG. 13 shows the test results. Looking at the test results, it can be seen that the treatment effect is improved by heating the resin molded article 10. It can also be seen that the conductive material of the counter electrode 20 is not affected much. The reason why the treatment effect can be improved by heating in this way is thought to be because, at higher temperatures, chemical reactions accompanying the treatment are accelerated and water, which is an obstacle to the treatment, is removed.

- Example 5 - In this example, the effect of cleaning the resin molded article 10 before performing the corona discharge treatment was confirmed. The basic processing conditions were the same as in Example 2 above. Specific cleaning methods include steam cleaning with trichloroethane (TCE) repeated twice in 30 seconds, and hand degreasing with a sponge scrubber using Kao Foaming (product name: Kao, commercially available cleaning agent). A method of cleaning with Surf Cleaner (trade name: Nippon Paint Co., Ltd., water-based detergent for resins) at 60° C. for 2 minutes was applied. As a result, when using either method, coating was applied to the resin molded article after corona discharge treatment and the peel strength of the coating film was measured, it was confirmed that the strength was significantly improved compared to the one that was not washed.

[0069]

Effects of the Invention According to the corona discharge treatment method and apparatus for resin molded products according to the present invention described above, by generating corona discharge using a high voltage pulse having the waveform as described above, spark discharge can be achieved. This makes it difficult for this to occur, and it becomes possible to bring the discharge electrode closer to the edge of the resin molded product. As a result, sufficient corona discharge treatment can be applied to the edges of resin molded products, where conventional methods could not perform sufficient corona discharge treatment, and uniform and good corona discharge treatment can be applied to the entire resin molded product. . In addition, compared to conventional methods, spark discharge is less likely to occur even when a higher voltage is applied, so it is possible to increase the applied voltage to achieve stronger processing effects and to perform processing more efficiently in a shorter time. This makes it possible to greatly contribute to improving the efficiency and performance of corona discharge treatment for three-dimensional resin molded products.

[Brief explanation of drawings]

[Fig. 1] A schematic configuration diagram of the entire device showing an embodiment of the present invention.

[Figure 2] Schematic diagram of pulse waveform used in this invention

[Figure 3] Waveform diagram showing a specific example of pulse waveform

[Figure 4
] Waveform diagram showing another specific example of pulse waveform

[Figure 5]
Cross-sectional diagram showing the specific structure of the discharge electrode and counter electrode

[Figure 6] Enlarged cross-sectional view of main parts showing another specific example of a discharge electrode

[Figure 7] Side view of Figure 5

[Figure 8] Explanatory diagram showing an example of voltage application state to the discharge electrode

[Fig. 9] Explanatory diagram showing another example of voltage application state to the discharge electrode

[Fig. 10] A schematic explanatory diagram showing a method of conducting a performance comparison test between the method of the present invention and the conventional method.

[Figure 11] Graph showing the results of the above performance comparison test

[
Figure 12: Graph showing performance comparison results due to differences in electrode structure and operation in this invention

[Figure 13] Graph showing the performance improvement effect of heating in this invention

[Explanation of symbols]

10 Resin molded products 20 Counter electrode 30 Discharge electrode 40 High voltage pulse power supply 50 Power supply section 60 Pulse forming section 90 Discharge load system

Claims (2)

[Claims] Claim 1: A resin molded product having a three-dimensional shape is placed between a discharge electrode and a counter electrode, and a high voltage is applied between both electrodes to generate a corona discharge, so that the surface of the resin molded product is A corona discharge treatment method for a resin molded product, characterized in that a corona discharge is generated by a high voltage pulse having a peak value of 10 to 100 kV, a pulse width of 1 μs or less, and a pulse frequency of 10 to 1000 pps. Discharge treatment method. 2. A resin molding having a three-dimensional shape, comprising a discharge electrode and a counter electrode disposed facing each other, and a high voltage power source that applies a high voltage between the discharge electrode and the counter electrode to generate corona discharge. In a corona discharge treatment apparatus that performs corona discharge treatment on the surface of a product, the high voltage power source includes a power supply section that generates high voltage direct current and a pulse forming section that converts the high voltage direct current into high voltage pulses, High price is 10-1
00kV, pulse width 1μs or less, pulse frequency 10~
A corona discharge treatment apparatus for resin molded products, characterized in that it is a high voltage pulse power source that generates high voltage pulses of 1000 pps.