JP2003292650A - Corona discharge treatment method, method and apparatus for producing plastic film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a plastic film which prevents a local development of a charged pattern to be caused by corona discharge treatment, and is hard to cause cissing and loss of a coating film in the posttreatment of coating and deposition, and is hard to cause creases and blocking. <P>SOLUTION: In the corona discharge treatment method by exposing the surface of a plastic film to corona discharge while bringing the plastic film into contact with a roll having a dielectric material layer on its surface, the surface potential of the above dielectric material layer is controlled. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a corona discharge treatment method and a corona discharge treatment device for a plastic film.

[0002]

2. Description of the Related Art Conventionally, secondary processing is performed by activating the surface of a sheet and improving the adhesiveness (paintability) in coating of printing ink, release agent, adhesive, etc. and vapor deposition typified by metal vapor deposition. Corona discharge treatment is widely known as a means for effectively treating the surface of a plastic film (for example, "Creating a polymer surface" edited by the Society of Polymer Science,
Listed in Kyoritsu Publishing).

As shown in FIG. 4, the above-mentioned document discloses a corona discharge treatment apparatus composed of a discharge electrode, a counter electrode roll covered with a dielectric layer and grounded, and a high-frequency high-voltage power supply. This device generates a corona discharge between the discharge electrode and the counter electrode roll by applying a high frequency voltage between the discharge electrode and the counter electrode roll. In this apparatus, a plastic film is moved along a counter electrode roll so as to pass through a corona discharge atmosphere, and a long object is continuously surface-treated.

This corona discharge treatment has the drawback of charging the object to be treated. Especially when the object to be treated is a plastic film, the volume resistance of the film is generally 10 ¹² Ωcm.
Because of the high cost, the film is easily charged, and the charge is likely to remain afterwards. The corona discharge treatment shows a locally distributed charging pattern. Such electrification causes defects such as repelling the coating solution and the vapor deposition film at the electrified portion being removed during the post-processing coating or vapor deposition process, or the plastic films blocking each other due to static electricity. , There was a production defect that caused wrinkles.

In order to solve the problems in production due to the corona discharge treatment, some techniques for removing the charge on the plastic film have been proposed.

For example, Japanese Unexamined Patent Publication (Kokai) No. 2-180935 discloses a method of neutralizing a plastic film by using a voltage application type neutralizer immediately after corona discharge treatment. However, although this static elimination method can reduce the potential of the entire plastic film, it is difficult to remove the locally electrified pattern.

Further, Japanese Patent No. 2651476 discloses a method of attracting positive and negative ions to a charged film or the like. However, although this static elimination method can remove the locally charged pattern to some extent, it has not been able to sufficiently remove defects such as blocking. The reason is that, in the static elimination method, since positive and negative ions can be actually supplied only from one surface side of the film or the like due to the device configuration, the inventor may inevitably remain charged on the other surface. Think about them.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to suppress the occurrence of a local electrified pattern due to corona discharge treatment while maintaining the conventional corona discharge treatment effect, and to prevent application repelling, film loss, wrinkles, blocking, etc. Is to eliminate.

[0009]

In view of the problems of the prior art as described above, the inventors of the present invention do not simply perform a static charge removal process on a film having a charged pattern, but generate a charged pattern. We paid attention to the fact that it should be eliminated from the root cause of.

As a result of earnest studies, the present inventors have found that one of the main factors causing this local electrification pattern is the electrification of the dielectric layer coated on the counter electrode roll. The mechanism is as follows. Generally, a counter electrode roll is provided with a dielectric layer on a conductor roll such as a metal for suppressing generation of spark discharge, but has a volume resistance of 10 ¹¹ Ωcm or more to improve electric insulation. The material is used. Both the plastic film and the dielectric layer of the counter electrode roll are materials that are easily charged. Moreover, the plastic film is strongly charged by passing through the corona discharge treatment atmosphere, and the dielectric layer of the counter electrode roll is also strongly charged by friction with the plastic film. The absolute value of the surface potential of the plastic film and dielectric layer is 2
It reaches over 0kV. Due to the potential difference due to the charging between the two, a discharge occurs between the plastic film and the dielectric layer at the position where the plastic film starts to wind around the counter electrode roll or the position where the plastic film separates from the counter electrode roll, and the discharge causes the discharge on the plastic film. Local charging occurs. Further, local charge remains on the dielectric layer, and when the counter electrode roll rotates and reaches the position where the plastic film starts to wind around the processing roll or moves away from the processing roll again, a secondary charge is generated between the dielectric film and the plastic film. Electric discharge occurs. Due to these discharges, a locally charged pattern is generated on the plastic film. This is supported by the observation result that a local electrification pattern is generated in the outer peripheral cycle of the counter electrode roll.

The present invention has been reached from such hypotheses and findings.

That is, according to the present invention, a plastic film is brought into contact with a roll having a dielectric layer on its surface,
It is a corona discharge treatment method of exposing a corona discharge to the surface of the plastic film, wherein the surface potential of the dielectric is adjusted.

Further, the present invention is a method for producing a plastic film, which comprises a step of subjecting a plastic film to a corona discharge treatment by the above corona discharge treatment method.

The present invention further comprises an AC power source, a counter electrode roll having a grounded conductor roll coated with a dielectric layer, and a discharge electrode connected to the AC power source, and a plastic conveyed on the counter electrode roll. An apparatus for performing corona discharge treatment on a film, comprising a means for adjusting the surface potential of the counter electrode roll.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The corona discharge treatment method of the present invention comprises:
The plastic film is the object to be processed. The material of the plastic film to be processed is polyethylene,
Polyolefin such as polypropylene, polyester,
Examples include polycarbonate, polyimide, polyphenylene sulfide, and aramid. In particular, a film having low wettability requires corona discharge treatment in order to improve coatability and vapor deposition property, and polypropylene is a good target in this respect, and if the volume resistance is high, it is easy to be charged In this respect, a polyolefin film is a good target because it easily causes the above problem.

Corona discharge treatment is carried out by exposing the plastic film surface to corona discharge while bringing the plastic film into contact with a counter electrode roll having a dielectric layer on the surface.

As the dielectric layer coated on the counter electrode roll, a material having excellent heat resistance, ozone resistance and electrical insulation is generally used. In order to obtain this characteristic, for example, silicone rubber, ethylene propylene diene rubber (EPD)
M), Hypalon, ceramics, etc. are adopted. The electrical insulation property is preferably 10 ¹¹ Ωcm or more, but with such a resistance value, the dielectric coating layer is easily charged, which is a preferable target of the present invention. In particular, the present invention is more effective when the resistance value is 10 ¹³ Ωcm or more.

The discharge electrode for generating the corona discharge is
There are a knife edge shape, a plate shape, a traveling film having a projection, and a wire shape.

As the atmosphere gas for corona discharge, air, nitrogen, carbon dioxide or a mixed gas thereof can be used.

Further, in order to prevent the surface of the plastic film opposite to the corona discharge treated surface from being modified, a nip roll is provided at the place where the plastic film is wound around the counter electrode roll, and the nip roll is provided between the plastic film and the counter electrode roll. It can also be appropriately adopted to prevent air from entering as much as possible. In this case, since the film and the counter electrode roll strongly rub at the contact position of the nip roll, the dielectric coating layers of the film and the counter electrode roll are strongly charged, and the charging problem that is the subject of the present invention is likely to occur. When the nip roll is used in this way, the corona discharge treatment method of the present invention is more effective.

There is a parameter called discharge degree as an index of the strength of corona discharge. The discharge degree represents the electric power supplied per unit area of the discharge electrode, and can be represented by the following formula (1). Discharge degree (W / cm ² ) = Supply power (W) / Area of discharge electrode (cm ² ) ... (1) The area of the discharge electrode of the formula (1) means the area of the portion where the electrode is discharged. . However, when discharge light is observed on almost the entire electrode surface facing the film, it can be roughly estimated by the area of the projection surface when the electrode is simply projected on the film surface. When this discharge degree is 5 W / cm ² or more,
Discharge between the plastic film and the dielectric layer of the counter electrode roll is likely to occur, and a local electrification pattern is likely to occur. Therefore, the present invention is effective under the conditions of the above discharge degree.

In the present invention, it is important to adjust the surface potential of the dielectric layer of the counter electrode roll during corona discharge treatment. By doing so, it is possible to eliminate the occurrence of the charging pattern from the root cause.

As a means for adjusting the surface potential of the dielectric layer, a method of destaticizing the dielectric layer or a method of electrically disconnecting the conductor roll coated with the dielectric layer from the ground to remove the surface potential of the dielectric layer is used. A method of providing a means for applying a potential having a polarity opposite to that of can be preferably adopted.

As the static eliminating means, there are a voltage applying type, a voltage applying air blowing type, a self-discharge type, a soft X-ray type, an ultraviolet type and the like. Especially, the voltage applying type which produces a large amount of ions and the apparatus is compact. preferable.

Regarding the voltage application type, either an alternating current or a direct current can be adopted as the applied voltage, but the surface potential of the dielectric layer of the counter electrode roll is brought close to zero, or the surface of the dielectric layer in the axial direction of the counter electrode roll. In order to make the potential distribution more uniform, an AC voltage is preferable. In this case, the applied voltage is 4
It is preferable to set the voltage to -12 kV. If the voltage is too low, the amount of generated ions tends to be insufficient, and if the voltage is too high, problems such as spark discharge tend to occur. The distance between the static eliminator, which is a static eliminator, and the dielectric layer is 10 to 100.
The range of mm is preferred. If the gap is too narrow, the film tends to come into contact with the roll when troubles occur in winding, which tends to lead to device failure. If the gap is too wide, the generated ions tend not to be sufficiently supplied to the dielectric coating layer.

However, depending on the condition of corona discharge determined by the application of the plastic film, etc., it is possible to suppress the discharge generation due to the charging pattern by making the surface potential of the dielectric layer have a certain bias value instead of 0V. In this case, it is preferable to use a DC static eliminator or a DC voltage applying type charger as the surface potential adjusting means.

The amount of ions generated from the static eliminator or the charger is preferably 500 nA or more in absolute value in order to control the potential of the processing roll during rotation. The amount of ions can be measured using an ion ammeter (Ionometer ICM-2 manufactured by Simco) when the measurement gap is set to the distance from the static eliminator or the charger to the dielectric layer.

Further, by adjusting the surface potential, the absolute value of the surface potential of the dielectric layer is set to 10 kV or less in order to suppress the occurrence of electric discharge between the plastic film and the dielectric roll, which causes local electrification. preferable. A commercially available surface potential meter can be used for measuring the surface potential.

It is preferable to control the potential adjusting means so that the absolute value of the surface potential of the dielectric layer becomes a certain value or less according to the output of the surface electrometer. The control of the potential adjusting means can be performed by changing the voltage of the static eliminator or the charger or changing the distance between the static eliminator or the charger and the dielectric layer.

In the case of corona discharge treatment of a plastic film having a wide width of 5 m or more, for example, a plurality of surface electrometers are arranged so that the surface potential of the treated roll dielectric coating layer can be measured at a plurality of points in the width direction. Alternatively, it is effective to measure the surface potentials at a plurality of points on the dielectric layer by scanning the surface potential meter in the width direction. In this case, as a guide for controlling the potential adjusting means, a method of controlling the average value of the surface potential measurement values at a plurality of points in the width direction to a desired potential, or a potential adjusting means such as a static eliminator in the width direction is used. It is effective to control the potential at each position to an optimum value by dividing and controlling independently.

Further, preferably, the charge on the surface of the counter electrode roll can be weakened more effectively by removing the charge from the nip roll.

Next, an example of a polypropylene film will be shown for the preferred method for producing the film of the present invention.

A polypropylene resin having an isotactic index of 95% or more is supplied to an extruder at a temperature of 190 to 270 ° C., melted, and extruded in a sheet form from a flat die (T die) having slits, 20 to 20. 100
C., more preferably 40 to 90.degree. C., and cooled and solidified with a cooling roll. In this case, the surface roughness can be adjusted by selecting the temperature of the cooling roll. Then 1
It is stretched 3 to 6 times in the length direction at a temperature of 10 ° C to 150 ° C. In this case, the surface roughness can be adjusted by selecting the stretching temperature. Then, it is stretched 7 to 12 times in the width direction at a temperature of 150 to 170 ° C. Then 150
Heat treatment is performed at a temperature of 170 ° C. The polypropylene film may be stretched by either the tenter method or the inflation method. In addition to the sequential biaxial stretching as described above, simultaneous biaxial stretching or uniaxial stretching may be adopted. However, when it is required to have a small thickness or a small thickness unevenness like a film for capacitors, biaxial stretching by the tenter method is preferable. Thereafter, the film is subjected to the corona discharge treatment of the present invention as described above.

It is preferable that the plastic film after passing through the corona discharge treatment, that is, after passing through the counter electrode roll is further discharged. In that case, it is more effective if the charge removal is performed from the corona discharge treated surface (the surface opposite to the surface in contact with the counter electrode roll). It is preferable that the absolute value of the surface potential of the plastic film after this static elimination is 5 kV or less.

The film thus obtained may be wound with a winder and then cut with a slitter for use as a product. At this time, it is more preferable to reduce the surface potential on the film roll with an applied voltage of 5 to 12 kV by using a voltage application type static eliminator installed at a distance of 50 to 300 mm from the film in the winding section (winding part).

By the above method, a plastic film having no local electrified pattern on the plastic film can be obtained. Further, the desired treatment effect can be maintained without changing the conventional corona discharge treatment conditions.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

[Measurement / Observation Method] 1. Visualization of charged state A powder toner used in a printer or a copying machine was sprinkled on a corona-discharge-treated film for visualization.

[Example 1] A polypropylene film 5 having a thickness of 17 µm was subjected to a corona discharge treatment on one surface thereof using the corona discharge treatment device shown in Fig. 1 under the treatment conditions and charge elimination conditions shown below.

(Corona discharge treatment) Electrode shape: Four rows of knife-edge electrodes having a tip radius of 2.0 mm. Discharge degree: 6 W / cm ² Power frequency: 45 kHz Electrode-film gap: 1.0 mm Film speed: 50 m / min Counter roll: Stainless steel conductive roll 2 with dielectric layer 3 made of EPDM rubber having a thickness of 3.0 mm Coated with (volume resistance of EPDM rubber is 10 ¹⁴ Ωcm) Temperature / humidity: 20 ° C./50%.

(Electrification removal condition for counter electrode roll) Electrode: Needle electrode power supply voltage of cross section shown in FIG. 2: AC 7 kV Power supply frequency: 50 Hz Electrode-dielectric coating layer gap: 50 mm Ion current value: +1500 nA / -1100 nA
.

As a result of visualizing the charge state of the corona discharge treated polypropylene film, no noticeable charge pattern was present on the polypropylene film.

[Comparative Example 1] A corona discharge treatment was applied to one side of a polypropylene film under the same conditions as in Example 1 except that the counter roll was not neutralized. As a result of visualizing the charged state of the polypropylene film subjected to corona discharge treatment, it has a tree shape as shown in FIG. 3 and a length of 5 to 30 mm.
A plurality of charging patterns were observed.

[0044]

EFFECTS OF THE INVENTION According to the present invention, the occurrence of a local electrified pattern generated by corona discharge treatment is prevented in advance, and in the subsequent coating or vapor deposition, coating repellency or film omission is less likely to occur, and wrinkles or blocking is caused. Get a hard plastic film.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a corona discharge treatment method according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a voltage application type static eliminator used in one embodiment of the present invention.

FIG. 3 is an example of a locally charged pattern generated in a conventional corona discharge treatment method (Comparative Example 1).

FIG. 4 is a schematic configuration diagram of a conventional corona discharge treatment method.

[Explanation of symbols]

1: Corona treated electrode 2: Conductive counter electrode roll 3: Counter electrode roll dielectric layer 4: High frequency power supply for corona treatment 5: Plastic film 6: Nip roll 7: Guide roll 11: Antistatic electrode for counter electrode roll potential control 12: High voltage power supply for static eliminator 13: Surface electrometer 14: Electrostaticizer electrode for plastic film 15: High voltage power supply for static eliminator 16: Needle electrode 17: Guard electrode 18: Resin 21: Local charge pattern

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05F 3/04 H05F 3/04 AZ // C08L 101: 00 C08L 101: 00 F term (reference) 4F073 AA01 BA07 BA08 BA23 BA26 BA29 BA30 BA31 BA32 BB01 CA21 CA25 CA27 CA30 CA31 HA12 4F209 AA11 AC03 AD08 AD32 AG01 PA13 PB02 PC16 PC20 PN20 PQ01 PW50 4G075 AA30 BA05 BC06 CA18 CA80 5G067 AA23 AA25 DA01 DA19

Claims (14)

[Claims] 1. A corona discharge treatment method of exposing a corona discharge to the surface of the plastic film while bringing the plastic film into contact with a roll having a dielectric layer on the surface, wherein the surface potential of the dielectric layer is adjusted. A corona discharge treatment method characterized by the above. 2. The corona discharge treatment method according to claim 1, wherein the surface potential of the dielectric layer is adjusted by discharging the dielectric layer. 3. The corona discharge treatment method according to claim 1, wherein the surface potential of the dielectric layer is measured and the surface potential of the dielectric layer is adjusted so as to be equal to or lower than a predetermined potential. 4. The corona discharge treatment method according to claim 3, wherein the surface potential of the dielectric layer is adjusted so that the absolute value of the surface potential of the dielectric layer is 10 kV or less. 5. The corona discharge treatment according to claim 1, wherein the inner layer of the roll has a conductive roll, and the surface potential of the dielectric layer is adjusted by applying a voltage to the conductive roll. Method. 6. A method for producing a plastic film, comprising the step of subjecting a plastic film to a corona discharge treatment by the corona discharge treatment method according to claim 1. 7. The method for producing a plastic film according to claim 6, wherein the plastic film after passing on the roll is further neutralized. 8. An AC power source, a counter electrode roll having a grounded conductor roll coated with a dielectric layer, and a discharge electrode connected to the AC power source, for a plastic film conveyed on the counter electrode roll. An apparatus for performing a corona discharge treatment, comprising a means for adjusting the surface potential of the counter electrode roll. 9. The corona discharge treatment apparatus according to claim 8, wherein the means for adjusting the surface potential of the counter electrode roll is a static eliminator. 10. The corona discharge treatment device according to claim 9, wherein the static eliminator is of a voltage application type. 11. The absolute value of the ion current of the static eliminator is 500 n.
It is A or more, The corona discharge treatment apparatus apparatus of Claim 9 or 10 characterized by the above-mentioned. 12. The corona discharge treatment device according to claim 8, further comprising surface potential measuring means of the counter electrode roll. 13. The volume resistance of the dielectric layer of the counter electrode roll is 10.
The corona discharge treatment device according to any one of claims 8 to 12, which has a resistance of ¹¹ Ωcm or more. 14. A means for neutralizing the surface of a nip roll attached to the counter electrode roll, further comprising:
13. The corona discharge treatment device according to any one of 13.