JP2010043215A - Surface treatment device for electric insulating sheet, surface treatment method, and method for producing electric insulating sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem: an optical defect is not suppressed according to a surface modification method using a discharge treatment of an electric insulating film, because an uneven coating tends to occur in an area having low wettability in a coating film for an optical film or the like, due to the uneven wettability of the film. <P>SOLUTION: The surface of the film is coated with a coating liquid after the discharge treatment using discharge density of 1×10<SP>4</SP>to 4×10<SP>4</SP>W/m<SP>2</SP>and treatment time of 0.04 to 0.2 second. Repelling of the coating liquid is less likely to occur and a coating defect is less likely to occur because of the uniform and even wettability of the surface of the film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrical insulating sheet surface treatment apparatus, a surface treatment method, and an electrical insulating sheet manufacturing method.

  The electrically insulating sheet is called a plastic film or simply a film. Hereinafter, the electrically insulating sheet is referred to as a film. Polyester films are widely used as various optical films because of their excellent transparency, dimensional stability, and chemical resistance. Excellent strength and dimensional stability, especially in applications such as prism lens base films, touch panel base films, backlight base films, and anti-reflection film (AR film) base films used in liquid crystal display devices Therefore, a relatively thick polyester film having a thickness of 50 μm or more is preferably used.

  These various optical films facilitate post-processing such as prism lens processing, hard coat processing and AR processing, and in order to ensure the adhesion between the processed thin film and the film, an easy-adhesion coating is applied to the surface of the base film. We are carrying out. In this coating, the molten resin is closely cooled and solidified on a cooling medium and processed into a sheet shape, and the cooled film is unstretched or stretched in a uniaxial direction and then coated on the film surface. Subsequently, the coated film was stretched in the width direction after drying a solvent such as water in a preheating zone in the tenter of the width direction stretching machine. This is called an inline coat.

  When an in-line coated film is used for optical applications, there will be a major problem if there is coating omission or coating unevenness of the coating layer. This is because post-processing is performed on the coating layer of the base film, so that the omission and uneven coating of the base film cause optical defects. In order to prevent omission of coating and uneven coating of the base film, it is important to easily wet the coating liquid and the film as the base material.

  According to Patent Document 1, the type of resin contained in the coating liquid to be coated is selected, the coating liquid is improved by using an aqueous coating liquid containing 50% by weight or less of isopropyl alcohol as a solvent, and the wettability to the film is improved. It has improved. The surface tension of isopropyl alcohol is as low as about 20 mN / m, which is smaller than the surface tension of water, 72 mN / N, and the wettability of the coating liquid to the film is improved.

  On the other hand, a technique for improving the wettability of a film as a base material and preventing coating omission and coating unevenness has been conventionally known. One method for improving the wettability of the film surface is corona treatment. Corona treatment has the advantage that the film, which is the object to be treated, is processed in a non-contact manner by utilizing electric discharge, so that the film is less likely to be scratched. There is an advantage that a film moving at a high speed can be processed as compared with the atmospheric pressure plasma processing. FIG. 4 is a schematic configuration diagram of a conventional corona treatment apparatus. The corona treatment apparatus includes a high frequency power supply 10, a counter electrode roll 34, and a discharge electrode 31. The film travels in close contact with the counter electrode roll 34, and travels through the gap between the discharge electrode 31 and the counter electrode roll 34 facing the counter electrode roll from left to right in the figure. A high frequency power supply 10 is connected to the discharge electrode 31 by a high voltage cable 11. Corona discharge is generated at the tip of the discharge electrode 31 due to the potential difference between the discharge electrode 31 and the counter electrode roll 34, the film surface is treated, and the wettability of the film is improved. The discharge electrode 31 has a great influence on the processing efficiency of the corona treatment and the uniformity of the treatment.

  The discharge electrode 31 has a shape in which the tip of the discharge electrode faces the counter electrode roll and is continuous in the film width direction, and the tip of the discharge electrode as viewed from the direction perpendicular to the film running direction has a knife shape. Since the knife-like discharge electrode 31 has a sharp tip, an electric field is excessively concentrated on the tip of the discharge electrode 31 and unstable discharge is likely to occur. In particular, when the voltage applied to the discharge electrode 31 is increased and the supply power is increased, a spark-like discharge is intermittently mixed so as to crawl the peripheral surface of the counter electrode roll 34 in the reddish purple corona discharge. Become. A spark-like discharge occurs intermittently because a large current flows locally and it is difficult to obtain sustained energy. For this reason, the discharge is not stable, the concentration of positive and negative ions and radicals is non-uniform, the surface treatment uniformity tends to be insufficient, and sufficient wettability cannot be improved, so this must be prevented. .

  Accordingly, in order to have a good surface treatment effect and to perform a uniform corona discharge treatment without unevenness, a corona structure comprising a metal discharge portion 43 shown in FIG. 5 and a rotatable earth roll 46 whose surface is coated with a dielectric is shown. A processing apparatus is disclosed in Patent Document 2. The shape of the discharge electrode 43 is a shape in which the tip of the discharge electrode has a smooth curvature in the cross section of the discharge electrode viewed from the direction perpendicular to the film running direction. The discharge electrodes 43 are parallel to each other, and the tips 42 of the respective discharge electrodes are protruded outward from each other in a bulging shape having a round cross-section of a semicircle or more. A configuration in which a plurality of discharge electrodes 43 are provided is disclosed.

   However, according to the knowledge of the present inventors, when the discharge electrode 43 of Patent Document 2 is used, the tip 42 has a bulging shape with a round shape of more than a half circle and protrudes outward from each other. Corona discharge generated simultaneously from the tip 42 of the discharge electrode toward the circumferential surface of the earth roll 46 tends to spread from the tip 42 to the circumferential surface of the earth roll 46. For this reason, when the supply power is increased in order to enhance the effect of the treatment, a spark-like discharge that crawls the peripheral surface of the earth roll 46 may be intermittently mixed. Conventionally, corona treatment has been carried out in order to improve the adhesion and printability of the film surface, and even if there is some variation in wettability, the adhesion and printability were not affected. However, in coating on a film for optical use, sufficient wettability and uniformity thereof are more important than before, and uneven coating due to variation in wettability may be a problem. In particular, when a plurality of discharge electrodes 43 are provided, non-uniform discharge spreading from the respective discharge electrodes 43 overlaps, and it is difficult to obtain a uniform discharge state as a whole. As a result, the wettability of the film is improved uniformly. There was a case that could not be done.

Patent Document 2 does not describe the power to be supplied, but the power supplied to the corona treatment is disclosed in Patent Document 3. According to Patent Document 3, an appropriate value of discharge density [W / m ² ] = supply power [W] / discharge electrode area [m ² ], which is power supplied per unit area of supplied power, is disclosed. Yes. In this, it is described that in order to improve the wettability of the film, for example, it is necessary to perform a strong corona discharge treatment with a discharge density of 9 × 10 ⁴ [W / m ² ] or more. On the other hand, it is described that when the discharge density is as small as 4 × 10 ⁴ [W / m ² ], the surface wettability is not sufficiently improved. That is, when the discharge density is 4 × 10 ⁴ [W / m ² ] or less, it is difficult to improve the wetting of the film surface, and a sufficient corona treatment effect cannot be obtained.

As described above, in the prior art, it has been difficult to obtain sufficient wettability on the film surface with high uniformity over the entire film surface. For this reason, in the coating film such as an optical film, the wettability is non-uniform, so that coating unevenness is likely to occur in a portion with low wettability, and the optical coating unevenness defect that can be visually confirmed cannot be suppressed.
JP 2002-205365 A Japanese Patent No. 2799698 JP 2001-59033 A

  Problems to obtain sufficient wettability on the film surface with high uniformity over the entire film surface are as follows.

  That is, the surface wettability is improved by the corona treatment. For example, in order to obtain the effect of improving the wetting tension, which is one of the characteristic values, the supply power for processing the film must be large. , The spark-like long discharge is mixed intermittently, and the discharge becomes non-uniform. For this reason, it is difficult to obtain uniformity of wetting of the film surface. This non-uniform discharge is less likely to occur, and the film can be processed by stable corona discharge even when a plurality of discharge electrodes are provided. That is, the problem to be solved by the present invention is that the corona treatment effect is high even with a small supply power, and the film surface is treated with high uniformity even when a plurality of discharge electrodes are used. Another object of the present invention is to provide a surface treatment apparatus, a surface treatment method, and a method for producing an electrical insulating sheet made of a film having a stable quality, eliminating the problems of the prior art. is there.

  The configuration of the present invention for solving the above-described problems is as follows.

That is, according to the present invention, a method for forming a discharge region by applying a high-frequency electric field between the discharge electrode tip and the counter electrode roll, and moving the electrically insulating sheet to the discharge region to treat the surface of the electrically insulating sheet. The discharge density is 1 × 10 ⁴ [W / m ² ] or more and 4 × 10 ⁴ [W / m ² ] or less, and the time for the electrically insulating sheet to pass through the discharge region is 0.04 [ A surface treatment method for an electrically insulating sheet that is not less than seconds and not more than 0.2 seconds is provided.

According to another aspect of the present invention, there is provided a method for producing an electrical insulating sheet, wherein a high frequency electric field is applied between a discharge electrode tip and a counter electrode roll to form a discharge region, and the electrical insulating property is formed in the discharge region. In the method of moving the sheet to treat the surface of the electrical insulating sheet, the discharge density is 1 × 10 ⁴ [W / m ² ] or more and 4 × 10 ⁴ [W / m ² ] or less, and the electrical insulating property Production of an electrically insulating sheet using a surface treatment method in which the sheet passes through the discharge region for a time of 0.04 [sec] or more and 0.2 [sec] or less, and subsequently coats the electrically insulating sheet with a coating solution. A method is provided.

According to another aspect of the present invention, there is provided a method for producing an electrical insulating sheet, wherein the molten resin sheet is brought into close contact with a cooling medium to be cooled and solidified to form an electrical insulating sheet, and the surface of the electrical insulating sheet Furthermore, the discharge density is 1 × 10 ⁴ [W / m ² ] or more and 4 × 10 ⁴ [W / m ² ] or less, and the time for which the electrical insulating sheet passes through the discharge region is 0.04 [second] or more. After performing a discharge treatment of 0.2 [sec] or less, and subsequently coating the electric insulating sheet with a coating liquid with a thickness of 3 [μm] or more and 30 [μm] or less, at least the electric insulating sheet is arranged in the width direction. A method for producing a stretched electrically insulating sheet is provided.

  Moreover, according to the preferable form of this invention, the manufacturing method of the electrical insulation sheet which uses an optical use sheet as an electrical insulation sheet is provided.

  Moreover, according to another aspect of the present invention, there is provided an electric having a discharge electrode provided on one side of the electrical insulating sheet and a counter electrode roll provided on the other side so as to face the discharge electrode. A surface treatment apparatus for an insulating sheet, wherein the plurality of discharge electrodes arranged in the traveling direction of the electrical insulating sheet each have a discharge electrode tip portion facing the counter electrode roll, and each discharge electrode tip portion Is a part of a cylinder extending in the width direction of the electrically insulating sheet, and the cross section of the cylinder at the tip of the adjacent discharge electrode has a diameter Rn-1 [mm] and a diameter Rn [mm] (n is a natural number). 0.25 ≦ [(Rn−1 + Rn) / 2] /d≦0.5 holds at the center distance d [mm] between adjacent discharge electrode tips, and On the cross-section of adjacent cylinders at the tip of multiple discharge electrodes It takes the sum D [mm] is 35 [mm] or more 100 [mm] or less is a surface treatment apparatus of the electrically insulating sheet of each circle center distance is provided.

  Moreover, according to the preferable form of this invention, the gap of the outermost position of the front-end | tip part of the said opposing discharge electrode and the outermost position of the said counter electrode roll is 1.5 [mm] or more and 4 [mm] or less. An insulating sheet surface treatment apparatus is provided.

  Further, according to a preferred embodiment of the present invention, each of the diameters Rn-1 and Rn (n is a natural number) is 2 [mm] or more and 5 [mm] or less in the cylindrical cross section of the adjacent discharge electrode tip. An insulating sheet surface treatment apparatus is provided.

The “discharge density” in the present invention relates to the intensity of the discharge for performing the corona treatment, and the supply power [W] applied to the discharge is measured when the discharge electrode is projected in the counter roll direction. It is the intensity of discharge per unit area divided by area [m ² ]. The supplied power [W] required for the discharge is the power on the primary side of the high-frequency power source. The area of the discharge electrode refers to the area of the portion of the electrode surface that is discharged. However, when the discharge light is observed on almost the entire electrode surface facing the film, it is calculated as the area of the projection surface when the electrode is projected onto the film surface. In the case of a plurality of discharge electrodes, it is the sum of the projected areas of the discharge electrodes.

  The “time to pass through the discharge region” in the present invention is the time for which the film as the electrically insulating sheet is exposed to the corona discharge treatment, and is the time taken to pass through the corona treatment atmosphere. The time required for passing through the corona treatment atmosphere is the total distance between the centers of the circles corresponding to the cross section of the cylinder in a part of the cylinder extending in the film width direction at the tip of each discharge electrode. Time [sec] when divided by [m / sec]. The “corona discharge treatment atmosphere” is a gas space in which a large number of radicals and positive and negative ions created by corona discharge exist. In the present invention, the length of the “corona discharge treatment atmosphere” in the film moving direction substantially coincides with the sum of the distances between the centers of the respective discharge electrode tips.

  Typical examples of the electrically insulating sheet to which the present invention is applied are a plastic film, a fabric, and paper. As the film form, there are usually a long film that is handled in a rolled state, and a sheet film that is usually handled in a state where a large number of films are laminated. Examples of the plastic film include polyethylene terephthalate film, polyethylene naphthalate film, polypropylene film, polystyrene film, polycarbonate film, polyimide film, polyphenylene sulfide film, nylon film, aramid film, and polyethylene film. In general, a film has higher electrical insulation than a film made of other materials. Examples of the electrical insulating sheet include those in which a conductive thin film such as a metal is coated on one side in advance.

  ADVANTAGE OF THE INVENTION According to this invention, the subject of a prior art is eliminated and the corona treatment apparatus with a favorable processing effect is obtained even with low power supply. When the corona treatment apparatus of the present invention is used, the wettability of the film surface is sufficiently improved with high uniformity. When a coating solution is coated on the surface-treated film according to the present invention, coating defects are less likely to occur. For this reason, the manufacturing method of the roll body which consists of a stable quality film can be provided.

  Hereinafter, preferred embodiments of the corona treatment apparatus for an electrically insulating sheet of the present invention will be described with reference to the drawings. A case where a plastic film (hereinafter, simply referred to as a film) is used as the electrically insulating sheet will be described as an example. The present invention is not limited to these examples.

  FIG. 1 is a schematic view of a corona discharge treatment apparatus showing an embodiment of the present invention.

  In FIG. 1, a corona discharge treatment apparatus 1 includes a discharge electrode 2 and a counter electrode roll 6. A plurality of discharge electrodes 2 provided on one side of the film are formed, and each discharge electrode 2 has a discharge electrode tip 3. The discharge electrode tip 3 is disposed in a state of facing the counter electrode roll 6, and each discharge electrode tip is a part of a cylinder extending in the film width direction. Therefore, when viewed from the traveling direction of the film S, the discharge electrode tip 3 of the discharge electrode 2 has a continuous shape. Further, when the discharge electrode tip 3 is viewed from a direction perpendicular to the traveling direction of the film S, the cross section is a part of a cylinder, and is connected to the discharge electrode 2 at the upper part of the cylinder. The outermost position of the discharge electrode tip 3 is opposed to the outermost position of the counter electrode roll 6 with an interval of 1.5 mm to 4 mm. Each discharge electrode 2 and discharge electrode tip 3 is made of a metal conductor, but a dielectric or the like may be coated on the surface layer of the metal conductor as necessary. The covering material is preferably a dielectric, and is preferably excellent in heat resistance and durability. Generally, “Teflon (registered trademark)” or ceramics is used. In the plurality of discharge electrodes, it is preferable that the gap between the outermost position of the tip portion of the opposing discharge electrode and the outermost position of the counter electrode roll is substantially matched in each form.

  In FIG. 1, eight discharge electrodes 2 are provided side by side with the insulating electrode holder 9 facing the counter electrode roll 6. Each discharge electrode 2 is electrically connected to a high frequency power supply 10 by a high voltage cable 11. A high voltage transformer is installed between the high frequency power supply 10 and the discharge electrode 2 (not shown). The electrode holder 9 and the plurality of discharge electrodes 2 are surrounded by an exhaust hood 8. The ozone generated by the corona discharge is forcibly exhausted from the exhaust port 7 (exhaust equipment is not shown). The counter electrode roll 6 is a roll in which the dielectric layer 4 is formed on the outermost layer of the metal core 5 and is rotatable.

  The discharge electrode 2 and the counter electrode roll 6 are opposed to each other while maintaining a gap between the outermost position of the tip portion of the opposing discharge electrode and the outermost position of the counter electrode roll, and the film to be treated is disposed between the discharge electrode 2 and the counter electrode roll 6. You can drive between. One of the opposing discharge electrode 2 or counter electrode roll 6 is set to ground potential: 0 V. In FIG. 1, the core metal 5 of the counter electrode roll 6 is set to the ground potential. Since only the film surface on the discharge electrode 2 side is processed in the corona treatment, two sets of corona discharge treatment apparatuses 1 are provided in the traveling direction of the film S with the same configuration in order to treat both surfaces of the film. .

  FIG. 2 is a schematic view of a corona discharge treatment apparatus showing an embodiment of the present invention, and is a schematic view showing the corona discharge treatment apparatus 1 of FIG. 1 from the film running direction. In FIG. 2, the film S travels from the front to the back of the paper. A gap between the outermost position of the discharge electrode tip 3 and the outermost position of the dielectric layer 4 of the counter electrode roll 6 is a discharge gap 20. The discharge gap 20 is a distance between the outermost position of the opposed discharge electrode tip 3 and the outermost position of the counter electrode roll 6. Since each discharge electrode tip 3 is a part of a cylinder extending in the film width direction, the discharge gap 20 is adjusted to be a constant distance in the width direction of the film S as viewed from the film running direction. Yes. The discharge gap 20 is the shortest distance from a portion of the discharge electrode tip 3 closest to the counter electrode roll 6 to the outermost surface layer of the counter electrode roll.

  FIG. 3 is an enlarged view of the discharge electrode 2 portion of the corona discharge treatment apparatus 1 of FIG. A plurality of discharge electrodes 2 are provided at a distance in the film running direction. The cross-sectional shape of the discharge electrode tip 3 of each discharge electrode 2 is a circle or a part of a circle. The cylinder is continuous in the direction perpendicular to the film running direction, and the diameter of the circle in the cylindrical section is a constant value in the film width direction. In the cross-sectional shape of each discharge electrode tip 3, the diameter of the circle is Rn [mm] (n is a natural number). The diameters of the circles in the cross section of the adjacent discharge electrode tip 3 are Rn-1 [mm] and Rn [mm], and the distance between the centers of the circles in the cross section of the discharge electrode tip 3 is d. In the case where n discharge electrodes 2 are provided, the diameter of the circle in the cross section of the pole tip 3 by the discharge of each discharge electrode 2 from the upstream in the film moving direction is set to R1, R2, R3,. And the center-to-center distances of the respective discharge electrode tips 3 are d1, d2,. The total distance D between the centers of the respective discharge electrode tips 3 is represented by D = d1 + d2 +... + Dn−1, and is substantially the same as the length of the “corona discharge treatment atmosphere” in the film moving direction. Concerning the configuration of the diameters Rn−1 and Rn2 of each discharge electrode tip 3, the center distance d of each discharge electrode tip 3, and the sum D of the distances between centers of each discharge electrode tip 3, which exhibit the effects of the present invention. Will be described later.

  The high frequency power supply 10 supplies a voltage and a current necessary for causing a discharge between the discharge electrode 2 and the counter electrode roll 6. The frequency supplied from the high frequency power supply 10 is an AC frequency of 10 kHz or more, but a DC voltage may be superimposed on the AC frequency. The voltage waveform may include a sine wave or a harmonic.

  Next, the operation will be described. The film S travels from the upper left of FIG. 1, travels while being wound around the counter electrode roll 6 in the upper part of FIG. 1, and passes through the corona discharge treatment apparatus 1. The counter electrode roll rotates with the film S clockwise. After passing through the corona discharge treatment apparatus 1, the film S is peeled off from the counter electrode roll 6. Then, it travels while being wound around another counter electrode roll 6 that rotates counterclockwise in the lower part of FIG. 1, passes through another corona discharge treatment apparatus 1, and is peeled off from the counter electrode roll 6. Although not shown, it is also preferable to dispose a charge remover or dust remover downstream of the corona discharge treatment apparatus to remove charge or remove dust from the corona-treated film. In FIG. 1, the upper corona discharge treatment apparatus 1 and the lower lower corona discharge treatment apparatus are performed on both surfaces of the film S. However, only one surface may be processed as necessary. If necessary, for example, processing may be performed only on the film surface to be coated. If only one side is coated, processing on one side is performed. If coating is performed on both sides, processing on both sides is performed. You can use them properly.

  A high voltage signal is applied to the discharge electrode 2 of the corona discharge treatment apparatus 1 from a high frequency power source 10 through a high voltage transformer at a predetermined frequency, and a corona discharge is generated with a discharge light due to a potential difference between the discharge electrode 2 and the counter electrode roll 6. appear. Therefore, since corona discharge occurs, the distance between the discharge electrode 2 and the counter electrode roll 6 is usually as narrow as 4 mm or less. The film to be processed travels in a “corona discharge treatment atmosphere” formed in a gap gap between the outermost position of the discharge electrode 2 and the outermost position of the counter electrode roll 6.

  The corona discharge treatment atmosphere refers to the state of the space where the space between the discharge electrode 2 and the counter electrode roll 6 is activated by a gas in which many radicals and positive and negative ions created by corona discharge are present. When the corona treatment is performed with air in the atmosphere, oxygen molecules in the air are activated, and there are many oxygen radicals or highly oxidative ozone. Oxygen radicals and ozone collide with the surface of the film S, break hydrocarbon bonds, add oxygen radicals to carbon, and cause an oxidation reaction. Thereby, a highly hydrophilic hydroxyl group or carboxyl group is formed on the surface of the film S. The wettability of the film surface is improved by imparting a highly hydrophilic polar group to the film surface.

  Note that a static eliminator that uses corona discharge does not expose the film to the light-emitting discharge area, and in principle, generates ions by corona discharge only at the tip of a needle-like or thin wire-like discharge electrode. In general, the ion is used to neutralize the charging of the film. That is, the static eliminator and the static eliminator are different from the aforementioned corona discharge treatment atmosphere.

  The corona discharge treatment on the film S is performed for the following two coatings. One is the process for “in-line coating” in the middle of the film forming process in the film forming process in which the resin is melted and molded and then stretched in the vertical and horizontal directions. The other is performed for “offline coating” in which the film is once wound on a roll in a film forming process and then unwound again.

  The case where the corona treatment method of the present embodiment is performed for in-line coating in the optical film forming process will be described below. As the film S, a polyester film having high transparency is preferably used. For optical films with high light transmittance and few optical defects, high-precision filtration is performed during melt extrusion in order to remove foreign substances contained in the raw material resin of the film.

  The molten PET resin is extruded in a sheet form from a die onto a rotating cooling drum, brought into close contact with the cooling drum, rapidly cooled and formed into a film, and then separated from the cooling roll. The obtained unstretched film is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120 ° C. to obtain a uniaxially stretched film.

  FIG. 7 is a schematic view of a process including a corona treatment device and a coating device. In FIG. 7, a coating device 47 is provided downstream of the two corona treatment devices 1 in the film traveling direction. In FIG. 7, after corona treatment is performed on both surfaces of the film, the film moves while being reversed in the film traveling direction by the transport roll 50, and is sent to the coating device 47. A coating liquid 48 is supplied to the coating apparatus 47 (a supply apparatus is not shown), and the coating liquid is thinly attached to the surface of the film S.

  After the uniaxially stretched film is subjected to the corona treatment of the present embodiment, the film is subsequently run to the coating process, and the coating liquid is coated on each surface of the film S on which the corona treatment has been performed, thereby forming a coated film. The coating in this case is performed for the purpose of imparting easy adhesion to the film to improve adhesion in the customer's post-process, and improving slipperiness to improve the running property of the film. The coating thickness (wet thickness) is preferably 3 to 30 μm.

  Furthermore, the film S is gripped by a clip, guided to a hot air zone heated to 70 to 140 ° C., and stretched 2.5 to 5.0 times in the width direction. In the case of the in-line method, the drying process of the coating liquid may be performed simultaneously with the stretching heating in the width direction.

  The coating coating solution is not particularly limited to a solvent system, but an aqueous coating solution is preferable from the viewpoint of working environment and environmental protection. A plurality of resins or the like may be added to the coating liquid. In order to impart other functions such as handling property, antistatic property and antibacterial property to the coating liquid, inorganic and / or organic particles, antistatic agent, ultraviolet absorber, organic lubricant, antibacterial agent, Additives such as a photo-oxidation catalyst can be included. Further, an anionic, nonionic or cationic surfactant may be added in an amount of 10% by weight or less. When a surfactant is added to the coating liquid, the wettability with the film is improved, but there is a concern that bubbles generated in the coating liquid are difficult to disappear.

  An optical defect of a film used as an optical film is a level of whether it is visible or invisible, and when the demand is severe, a size of about 20 to 100 μm becomes a defect. For this reason, the coated film is required to have very high homogeneity. In order to achieve the homogeneity of the coating film, it is important that the wettability of the surface of the film S is very uniform and there is no unevenness or defect in the wettability.

According to the knowledge of the present inventors, a spark-like discharge having a long leg that crawls the counter electrode roll 6 as described above is likely to occur in the following cases.
(1) When the gap between the outermost position of the discharge electrode 2 and the outermost position of the counter electrode roll 6, that is, the discharge gap 20 is large.
(2) When the discharge electrode 2 is sharp, such as a knife type or blade type, and the electric field is extremely concentrated at the tip of the discharge electrode.
(3) When the discharge density is high.
(4) When a plurality of discharge electrodes are provided to increase the supply power.

  Next, the area of the discharge electrode 2 and the shape of the discharge electrode 2 of the present embodiment in which such a discharge is unlikely to occur will be described.

  First, with regard to (1), in a spark-like discharge having a long leg that crawls the counter electrode roll 6, the discharge gap 20 between the outermost position of the discharge electrode 2 and the outermost position of the counter electrode roll 6 is 4 [mm] or less. It is hard to occur at the time of. If the discharge gap 20 between the outermost position of the discharge electrode 2 and the outermost position of the counter electrode roll 6 exceeds 4 mm, the electric field is weak and it is difficult for discharge to occur. Corona discharge is generated by concentrating the electric field. For this reason, spark-like discharge is intermittently generated, variation in wetting occurs, and uniformity is not sufficient. On the other hand, if the discharge gap 20 is too small, the discharge electrode 2 and the film S come into contact with each other due to thermal expansion or roll eccentricity, and the film is torn or scratched, thereby degrading the quality of the film. In general, the thickness of the optical film is 0.1 to 1 mm, but a gap of at least 1.5 [mm] or more is necessary. Therefore, the gap between the discharge electrode 2 and the counter electrode roll 6 is preferably 1.5 [mm] or more and 4 [mm] or less.

  Next, for (2), it is effective that the tip of the discharge electrode 2 has a rounded curvature rather than a pointed shape. The tip shape 3 is effective when the diameter of a circle or a part thereof is 2 [mm] or more to 5 [mm] or less in the shape of the tip of the discharge electrode viewed from the direction perpendicular to the film longitudinal direction. It is. More preferably, 3 [mm] to 4 [mm] is effective. If it is less than 2 mm, the electric field tends to concentrate on the discharge electrode tip 3 as described above, and the wettability of the film tends to vary. If it exceeds 5 mm, the concentration of the electric field is weakened, the corona discharge becomes unstable, and the wettability of the film tends to vary. In addition, each discharge electrode front-end | tip part is a part of cylinder extended in the film width direction, and it is preferable that the cylinder continues in the film width direction.

  Next, (3) and (4) will be described. In the polyester film for optics, it is preferable that the wetting tension of the film surface at the time of coating is 55 [mN / m] or more. If the surface wetting tension is less than 55 [mN / m], minute coating unevenness may occur in the coating process, which may result in an optical defect. Although the wetting tension of the film depends on the type of coating liquid and the coating method, it is generally sufficient that the film has a high uniformity of 55 [mN / m] or more.

Conventionally, even if corona treatment is performed at a low discharge density, sufficient wettability cannot be obtained. Therefore, the wettability of the film S has been improved by performing corona treatment at a high discharge density. That is, in order to obtain a wetting tension of 55 [mN / m] or more, the discharge density was set to several tens of 10 ⁴ [W / m ² ] or more. However, when the discharge density is 10 × 10 ⁴ [W / m ² ], the electric field is too strong, and a long-sparking spark-like discharge is generated and the uniformity of wetting is impaired. The inventors of the present invention have, for example, the relationship between the electrode shape and electrode arrangement capable of improving the wettability of the film and the time of exposure to the corona discharge atmosphere even at a discharge density as low as 4 × 10 ⁴ [W / cm ² ] or less. I found.

  The discharge density represents the power supplied per unit area of the discharge electrode, and is represented by the formula (1).

Discharge density [W / m ² ] = Supply power [W] / Discharge electrode area [m ² ] (1)
According to Equation (1), it can be seen that the discharge density decreases as the discharge electrode area increases. Therefore, if the discharge area is increased and the discharge density is decreased, the variation in wet tension can be suppressed. As described above, when the tip of the discharge electrode is a circle or a part thereof, a diameter of 2 [mm] to 5 [mm] is effective. Therefore, it is possible to increase the discharge area by arranging a plurality of discharge electrodes. preferable.

  In order to achieve this embodiment, when a plurality of discharge electrodes are provided, the spread of corona discharge at each discharge electrode tip 3 is controlled. When the gap between the discharge electrode 2 and the counter electrode roll 6 is 1.5 [mm] or more and 4 [mm] or less, and the shape of each discharge electrode tip 3 is a circle or a part thereof, the diameter of the circle is 2 [ In the case of mm] to 5 [mm], the spread of corona discharge is preferably 2 to 4 times the diameter R of the discharge electrode tip 3. The spread of the corona discharge varies depending on the power supplied to the discharge electrode 2. The larger the power supplied to the discharge electrode 2, the more the corona discharge spreads on the counter electrode roll, and the more likely the spark-like corona discharge that crawls the long film. If the spread of corona discharge is in the range of 2 to 4 times the diameter R of the discharge electrode tip 3, it is preferable because a long-sparking discharge that makes the wetting uneven can be avoided. If the spread of the corona discharge exceeds 4 times the diameter R, a long-sparking spark discharge that makes the wetting uneven will occur.

On the other hand, the smaller the supplied power, the smaller the spread of the corona discharge, but the “corona discharge treatment atmosphere” is not formed between the adjacent discharge electrode tips 3 and the uniformity of the corona treatment is poor and the wettability is sufficient. Does not rise. Furthermore, if the supplied power is too small, the entire region of the discharge electrode tip 3 is not stably discharged, the corona treatment is not uniform, and the wettability of the film surface does not increase.
If the adjacent discharge electrode tips 3 are too close, ie, less than twice the diameter R of the discharge electrodes tip, the distance between the discharge electrodes tip 3 is too narrow and abnormal discharge is likely to occur. For this reason, the spread of the corona discharge from each discharge electrode tip 3 is suitably 2 to 4 times the diameter R of the discharge electrode tip 3.

  When a plurality of discharge electrodes are provided, overlapping discharges of adjacent discharge electrodes causes non-uniform corona treatment. The distance d between the centers of adjacent discharge electrode tips is 2R to 4R (R is the diameter. The diameter of adjacent discharge electrodes is the same) in each discharge electrode, and R to 2R are added on both sides. Therefore, 2R ≦ d ≦ 4R, and 2 ≦ d / Rn ≦ 4 is obtained. In the interval between the diameter of the discharge electrode and the adjacent discharge electrode 2, the average value of the diameter Rn-1 [mm] and the diameter Rn [mm] of the adjacent discharge electrode tip 3 is between the centers of the adjacent discharge electrode tips. When the distance d [mm] and 0.25 ≦ [(Rn−1 + Rn) / 2] /d≦0.5 are satisfied, the discharge overlap between the adjacent discharge electrodes is not strong and the wetting is uneven. It has been found that a long spark-like discharge can be avoided, and that the film S has no uneven surface tension and can be processed with high uniformity.

  In order to sufficiently increase the wetting of the film S, the problem can be solved by increasing the treatment time for performing corona discharge even if the discharge density remains small. If the discharge electrode 2 becomes larger, the time required for the film S to pass under the discharge electrode becomes longer, and it is exposed to the corona treatment atmosphere for a longer time. However, even if the discharge electrode is simply enlarged, it is difficult to adjust the discharge gap 20 by mechanically increasing the size and facing the counter electrode roll. In the present embodiment, when a plurality of discharge electrodes are arranged at a center distance d [mm] between adjacent discharge electrode tips, 0.25 ≦ [(Rn−1 + Rn) / 2] /d≦0.5, The film S is exposed to corona discharge, not the actual length projected from the discharge electrode, but the total distance between the centers of the discharge electrodes, so that the processing time is the same for the same discharge electrode area. Can be earned efficiently about twice the actual length. For this reason, it discovered that film S was exposed to the corona treatment atmosphere for a long time, and sufficient wetting tension could be obtained. Under this condition, the uniformity of the wetting tension remains high as described above.

FIG. 6 is a characteristic diagram showing the treatment time and the wettability of the film S in the corona discharge treatment method according to an embodiment of the present invention. The treatment time on the horizontal axis was obtained by dividing the total length [mm] of the distance between the centers of the respective discharge electrode tips 3 by the moving speed [mm / second] of the film S. The vertical axis is a value obtained by measuring the wetting tension of the film S using a wetting reagent. When the discharge density exceeds 4 × 10 ⁴ [W / m ² ], a strong discharge that crawls the film occurs and the wettability of the film becomes non-uniform, so the discharge density is 1.5 × 10 for □. ⁴ [W / m ² ], ○ was 3 × 10 ⁴ [W / m ² ], and Δ was 4 × 10 ⁴ [W / m ² ]. From FIG. 6, the wetting tension of 55 [mN / m] or more is obtained at a discharge density of 4 × 10 ⁴ [W / m ² ] or less when the treatment time is longer than 0.04 [seconds]. Although the film S travels at approximately 20 [m / min] to 50 [m / min] depending on the process, in order to obtain a processing time of 0.04 [sec] or more, a plurality of discharge electrode tips The total D [mm] of the distances between the centers of the cylinders adjacent to each other is preferably 35 [mm] or more.

  The upper limit of the processing time is preferably 0.2 [seconds] or less because heat from the discharge electrode is radiated in proportion to the processing time. If the treatment time is increased beyond 0.2 seconds, depending on the type, oligomers are likely to precipitate on the film surface, which degrades the quality of the film. In addition, if the total distance D between the centers of the adjacent cylinders at the plurality of discharge electrode tips is too large, the discharge gap between the outermost position of the discharge electrode and the outermost position of the counter electrode roll is less likely to be a constant value. Therefore, 100 [mm] or less is preferable.

The lower limit of the discharge density is that when corona discharge begins to start over the entire width of the discharge electrode when the power supplied to the discharge electrode is gradually increased from the state where no corona discharge occurs between the discharge electrode and the counter electrode roll. The minimum discharge density. Less than 1 × 10 ⁴ [W / m ² ], although it depends on conditions such as the electrode shape, the gap between the outermost position of the tip of the opposing discharge electrode and the outermost position of the counter electrode roll, the counter electrode roll, and film characteristics Since no discharge is observed, this value is set as the lower limit.

In other words, a good film S having high wettability uniformity, the discharge density of ^{1 × 10 4 [W / m} 2] or more ^{4 × 10 4 [W / m} 2] or less, 0.04 [s] 0.2 [Seconds] This is achieved by performing the following corona discharge treatment. When this film S is coated, uneven coating is less likely to occur and a good coating film can be obtained.

[Example 1]
Hereinafter, the present embodiment will be specifically described with reference to examples. A polyester film was used as the film, and the wettability of the film was improved for in-line coating in the film forming process.

  Polyethylene terephthalate substantially free of particles is dried under reduced pressure at a temperature of 180 ° C. for 5 hours, and then supplied to an extruder, and then the molten PET resin is extruded from a die onto a rotating cooling drum in a sheet form, After closely contacting and rapidly cooling to form a film, the film was pulled away from the cooling roll. The obtained unstretched film was stretched 3.3 times in the longitudinal direction with a roll heated to 95 ° C. to obtain a uniaxially stretched film. The film thickness at this time was 450 μm. The moving speed of the film was 42 m / min.

  The uniaxially stretched film was subjected to corona discharge treatment and subsequently moved to the coating process, and the film surface subjected to the corona discharge treatment was coated with a coating solution.

  The coating liquid was an aqueous coating liquid, and included a polystyrene resin ammonium polystyrene and a polyester resin mixed at a weight ratio of 15/85 consisting of an acid component and a glycol component. The coating used a metering bar and the wet thickness was 10 μm. Furthermore, the edge part of the film S was hold | gripped with the clip, and it guide | induced to the hot air zone heated at 70-140 degreeC, extended | stretched 3.3 times in the width direction, and wound up finally.

  Corona discharge treatment was performed only on one side of the film. As the corona treatment apparatus, the corona discharge treatment apparatus 1 shown in the schematic configuration diagram at the top of FIG. 1 was used. AGI-030 (manufactured by Kasuga Denki) was used as a high-frequency power source, and was electrically connected to the discharge electrode and the high-voltage cable via a high-voltage transformer. The dielectric coating of the counter electrode roll 6 is made of high-paron rubber and has a rubber thickness of 5 mm. The core of the counter electrode roll 6 was made of SUS and was electrically connected to ground (0V). The discharge electrode 2 has a discharge electrode tip portion 3 that faces the counter electrode roll, and each discharge electrode tip portion is a part of a cylinder extending in the film width direction. The cross section has a shape including a part of a circle. The discharge electrode 2 was fixed with an insulating holder 9. The discharge electrode 2 is made of SUS, and eight identical ones are provided. The diameters of all the discharge electrode tips 3 were the same, and the diameters R1 to R8 [mm] of the cross-sections of the adjacent discharge electrode tips 3 were all 3 mm. The gaps d1 to d7 (referred to as center distances) when the centers of the cylinders of the adjacent discharge electrode tips 3 are connected to each other are 9 mm. The total distance between the centers of adjacent cylinders was 63 [mm]. The value of [(Rn-1 + Rn) / 2] / d (n = 1 to 8) was 1/3. The processing time was 0.09 [seconds]. The discharge gap 20 that is the gap between the outermost position of the opposing discharge electrode tip 3 and the outermost position of the counter electrode roll was set to 2.0 [mm]. The length in the length direction of the discharge electrode 2 was 1.2 m, and the length in the length direction of the counter electrode roll was 1.4 m.

The corona discharge treatment conditions were such that the voltage and current were adjusted so that the power supplied was 4 × 10 ⁴ [W / m ² ] at a frequency of 11 kHz from a high-frequency power source.

The following items were evaluated.
(1) The repelling state of the coating film The light of the fluorescent lamp was reflected on the coating liquid film, and the repellency in the undried state immediately after coating was observed with the naked eye, and judged according to the following two levels. The repelling means that the coating application surface is not smooth and has unevenness locally.

        Good: No repelling immediately after coating.

Defect: Flicking occurs immediately after coating, and unevenness is visible.
(2) Occurrence of coating unevenness of the coated film The coated film after drying was observed with an optical defect inspection apparatus, and judged according to the following two levels.

Good: Application unevenness on the coating film is 1 or less per 1 × 10 ⁻² m ² .

Defect: The coating unevenness on the coating film exceeds 1 per 1 × 10 ⁻² m ² .
(3) Wetting tension of film A film subjected to corona discharge treatment was collected without coating, and the wetting tension was measured using a wetting reagent (manufactured by Nacalai Tesque). The measurement temperature was 23 ° C. and the humidity was 50-55% RH.
(4) Uniformity of the wetting tension of the film As in the case of (3), a film subjected to corona discharge treatment was collected without coating, and the film (size A4) was 100 mm away from a pan filled with 90 ° C. distilled water. The state of adhesion of steam was visually observed, and the uniformity of the wetting tension was evaluated according to the following two levels.

Good: A4 size with no adhesion unevenness or 2 or less states Defect: A4 size with 3 or more uneven adhesions The results are summarized in Table 1.
[Example 2]
In Example 1, the number of discharge electrodes 2 was 6, and the diameters of all the discharge electrode tips 3 were the same, 3 mm. The distance between the centers of the adjacent cylinders of the discharge electrode 2 was 7 mm. The total distance between the centers of adjacent cylinders was set to 35 [mm]. The value of [(Rn-1 + Rn) / 2] / d was 3/7, approximately 0.43. The processing time was 0.05 [seconds]. Voltage so that the supply power becomes ^{3 × 10 4 [W / m} 2], and adjusting the current. Others were the same. The results are shown in Table 1.
[Comparative Example 1]
In Example 1, the number of discharge electrodes 2 was 8, and the diameters of all the discharge electrode tips 3 were the same, 3 mm. All the distances between the centers of adjacent cylinders of the discharge electrode 2 were 5 mm. The total distance between the centers of adjacent cylinders was set to 35 [mm]. The value of [(Rn-1 + Rn) / 2] / d was 0.6. The voltage and current were adjusted so that the supplied power was 4 × 10 ⁴ [W / m ² ]. Others were the same. The results are shown in Table 1. Since the distance between the centers of the adjacent cylinders of the discharge electrode 2 is too close, the discharge from each discharge electrode tip 3 becomes unstable, and the uniformity of the treatment effect cannot be obtained. The processing time was 0.05 [seconds].
[Comparative Example 2]
In Example 1, the number of discharge electrodes 2 was three, and the diameters of all the discharge electrode tips 3 were the same, 3 mm. The distances between the centers of adjacent cylinders of the discharge electrode 2 were all 9 mm. The total distance between the centers of adjacent cylinders was 18 [mm]. The value of [(Rn-1 + Rn) / 2] / d was 1/3, approximately 0.33. The processing time was 0.026 [seconds]. The voltage and current were adjusted so that the supplied power was 4 × 10 ⁴ [W / m ² ]. Others were the same. The results are shown in Table 1. The exposure time to the corona discharge treatment atmosphere was short, and high wettability was not obtained.
[Comparative Example 3]
In Comparative Example 2, the voltage and current were adjusted so that the supplied power was 10 × 10 ⁴ [W / m ² ]. Others were the same as in Comparative Example 2. The results are shown in Table 1. The electric field was concentrated on the tip of the discharge electrode, and a long-displaced discharge that crawls the film surface occurred, resulting in variations in the wettability of the film.
[Comparative Example 4]
A conventional corona treatment apparatus having the configuration shown in FIG. 4 was used. The discharge electrode was made of SUS, and was a knife-type discharge electrode with a tip width of 1 mm. The number of discharge electrodes was one. The corona treatment conditions were such that the voltage and current were adjusted so that the supplied power was 3 × 10 ⁴ [W / m ² ]. Others were performed in the same manner as in Example 1. Since the discharge density was small and the treatment time was short, the wettability of the film was not sufficiently improved.
[Comparative Example 5]
In Comparative Example 2, the voltage and current were adjusted so that the supplied power was 40 × 10 ⁴ [W / m ² ]. The electric field was concentrated at the tip of the discharge electrode, and a long-legged discharge that crawls the film surface occurred, resulting in variations in wettability. Moreover, the improvement of wettability was also insufficient.

  INDUSTRIAL APPLICABILITY The present invention can improve the wettability of the film with high uniformity without variation with respect to the coating of the film which is an electrically insulating sheet. As a base material, application to a sheet-like substrate such as glass and a circuit material substrate can be expected.

It is a schematic block diagram of the corona discharge processing apparatus which shows one embodiment of this invention. It is a schematic longitudinal cross-sectional view of the corona discharge processing apparatus which shows one embodiment of this invention. It is an enlarged view of the discharge electrode part of the corona discharge processing apparatus which shows one embodiment of this invention. It is a schematic block diagram of the corona treatment apparatus of a prior art. It is a schematic block diagram of the corona treatment apparatus of a prior art. It is a characteristic view which shows the processing time and the wettability of the film S in the corona discharge processing method which shows one embodiment of this invention. It is the schematic of the process which consists of a corona treatment apparatus and a coating apparatus.

Explanation of symbols

1: Corona discharge treatment apparatus 2: Discharge electrode 3: Discharge electrode tip part 4: Dielectric layer of counter electrode roll 5: Core metal of counter electrode roll 6: Counter electrode roll 7: Exhaust port (part of exhaust apparatus)
8: Exhaust hood 9: Insulating holder 10: High-frequency power source 11: High-voltage cable 20: Discharge gap 30: Corona treatment device 31 of prior art 31: Knife-type discharge electrode 33: Nip roll 34: Counter electrode roll layer 40: Different from the prior art Corona treatment device 42: Discharge electrode tip 43: Discharge electrode 44: Mounting device 45: Insulator 46: Earth roll 47: Coating device 48: Coating liquid 50: Conveying roll S: Electrical insulating sheet R1: Discharge electrode tip Diameter R2: Diameter of adjacent discharge electrode tips d: Distance between centers of adjacent discharge electrodes D: Total distance between centers of discharge electrodes

Claims (7)

A method of forming a discharge region by applying a high-frequency electric field between a tip portion of a discharge electrode and a counter electrode roll, moving the electrically insulating sheet to the discharge region, and treating the surface of the electrically insulating sheet, wherein a discharge density is 1 × 10 ⁴ [W / m ² ] or more and 4 × 10 ⁴ [W / m ² ] or less, and the time for the electrical insulating sheet to pass through the discharge region is 0.04 [second] or more and 0.2 [second]. ] A surface treatment method for an electrically insulating sheet, characterized in that: A method for producing an electrically insulating sheet, wherein a discharge region is formed by applying a high-frequency electric field between a discharge electrode tip and a counter electrode roll, and the surface of the electrically insulating sheet is moved to the discharge region The discharge density is 1 × 10 ⁴ [W / m ² ] or more and 4 × 10 ⁴ [W / m ² ] or less, and the time during which the electrically insulating sheet passes through the discharge region is 0. A method for producing an electrically insulating sheet, comprising using a surface treatment method of 04 [seconds] to 0.2 [seconds], and subsequently coating the electrically insulating sheet with a coating liquid. A method for producing an electrically insulating sheet, in which a molten resin sheet is brought into close contact with a cooling medium to be cooled and solidified to form an electrically insulating sheet, and a discharge density of 1 × 10 ⁴ [W / m ² ] or more and 4 × 10 ⁴ [W / m ² ] or less, and a time during which the electrically insulating sheet passes through the discharge region is 0.04 [second] or more and 0.2 [second] or less. Subsequently, after coating the electrical insulating sheet with a coating liquid with a thickness of 3 [μm] or more and 30 [μm] or less, at least the electrical insulating sheet is stretched in the width direction. Production method. The method for producing an electrical insulating sheet according to claim 2, wherein an optical use sheet is used as the electrical insulating sheet. A surface treatment apparatus for an electrically insulating sheet having a discharge electrode provided on one surface side of the electrically insulating sheet and a counter electrode roll provided to face the discharge electrode on the other surface side, The plurality of discharge electrodes arranged in the running direction of the electrically insulating sheet each have a discharge electrode tip portion facing the counter electrode roll, and each discharge electrode tip portion extends in the width direction of the electrically insulating sheet. A cross section of a cylinder at a tip portion of the discharge electrode adjacent to the discharge electrode is a part of a circle having a diameter Rn-1 [mm] and a diameter Rn [mm] (n is a natural number), and adjacent discharges. 0.25 ≦ [(Rn−1 + Rn) / 2] /d≦0.5 is satisfied at the center distance d [mm] between the electrode tip portions, and the cylinders adjacent to the plurality of discharge electrode tip portions are arranged. Total D [m] of the distance between each circle center in the cross section ] Is 35 [mm] or more 100 [mm] surface treatment apparatus of the electrically insulating sheet characterized by less. 6. The electricity according to claim 5, wherein a gap between an outermost position of a tip portion of the opposing discharge electrode and an outermost position of the counter electrode roll is 1.5 [mm] or more and 4 [mm] or less. Insulating sheet surface treatment equipment. The diameters Rn-1 and Rn (n is a natural number) are both 2 [mm] or more and 5 [mm] or less in the cylindrical cross section of the adjacent discharge electrode tips. Surface treatment equipment for electrical insulating sheets.

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