JP5557473B2 - Method and apparatus for manufacturing plastic film - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method and apparatus for producing a plastic film, and in particular, a film that maintains operational stability when an electrostatic adhesion method is employed in a cooling and solidifying process after extruding a molten resin from a die and has excellent quality. The present invention relates to a plastic film manufacturing method and apparatus capable of obtaining

  In a film forming process of a plastic film by a normal T-die method, a molten resin is extruded from a extruder through a T-die into a film shape, and the extruded film-like melt is rotationally driven called a casting roll. A method of cooling and solidifying by pressing against the surface of a cooling roll (hereinafter referred to as CR) is employed. Furthermore, the film formed by cooling is stretched in the longitudinal and lateral biaxial directions in the next stretching step, whereby a biaxially stretched plastic film is finally obtained.

  As a method of pressing the film-like melt on the CR surface, air is uniformly blown in the width direction by an air knife device, or an electrostatic charge is applied to the film-like melt from an electrode to which a high voltage is applied. There is a method (hereinafter referred to as an electrostatic contact method) in which the grounded CR is brought into close contact with an electrostatic force. This electrostatic contact method is widely used as an industrial means since it is excellent in cooling rate, thickness accuracy and quality uniformity of the formed film.

  In order to apply this electrostatic contact method to a continuous production line for plastic films, there is an operational problem that the electrodes must be periodically replaced. The reason is that vapors such as monomers and oligomers are generated from the molten resin extruded from the T-die, which adheres to the electrode and condenses, preventing uniform discharge of the electrode and non-uniform ionization of air around the electrode. This is because it causes a change over time in that the adhesiveness of the film-like melt decreases and surface defects due to adhesion spots occur.

  The most effective means for solving this operational problem is a method of sublimating the adhered monomer or oligomer by maintaining the temperature of the electrode at a temperature higher than the condensation temperature of the vapor generated from the molten resin. For example, Japanese Examined Patent Publication No. 47-29782 discloses a method in which a heater is heated to 250 ° C. or higher by passing a current directly through an electrode.

  As the speed of plastic film production lines in recent years increases, the total amount of electric charge necessary for electrostatic adhesion increases, so the voltage applied to the electrode must be increased to increase the discharge charge (current). However, simply trying to discharge the electrode at a high density leads to an unstable streamer corona discharge exceeding the uniform discharge capacity. Also, increasing the voltage beyond the spark limit increases the risk of spark discharge. However, by heating the electrode to a high temperature as described above, thermionic emission is promoted and a sufficient discharge current can be obtained at a low voltage. The electrode heated to a high temperature cannot be overlooked, as compared with the non-heated electrode, clearly has the advantage of having a low voltage easy discharge characteristic.

Japanese Patent Publication No.47-29782

  However, there is an inherent problem that cannot be avoided because the electrode is used as a heater for direct current flow.

  The electrode used for the electrostatic contact method is constructed by laying an electrode between left and right supports provided at intervals wider than the width of the film-like melt, and insulating sleeves on the outer sides of both ends of the film-like melt in this electrode. The discharge width from the electrode can be adjusted according to the width of the film-like melt. A DC high voltage power supply is connected to the electrode, and an electrode heating power supply is connected to the left and right ends of the electrode in a separate circuit.

  The electrode that is being discharged during operation is heated by the heater current, while the ion wind from the air discharge blows in the vicinity of the electrode, and the surrounding air passes through the wind and the wind speed of several tens m / s always passes. Heat is taken away. It is necessary to heat the electrode with a heater so that the equilibrium temperature between the heater heating and the ion air cooling is maintained at 250 ° C. or higher.

  However, since the electrode portion covered with the insulating sleeve and shielded from discharge is not cooled by the ion wind, it easily generates excessive heat. When the temperature is abnormally high, the electrode metal material is deteriorated at high temperature and the tensile strength is lowered. In order to avoid this, heater heating must be suppressed, and the temperature of the electrode could not be raised to a sufficiently high temperature.

  This phenomenon becomes a significant problem at high production speeds. That is, strong ion wind cooling acts in a situation where a high discharge current is required.

  A more troublesome problem is that the tip of the insulating sleeve is optimally positioned 5 to 10 mm inside the width direction of the melt from the left and right ends of the film melt so as not to directly spark discharge to the CR. If the electrode itself covered with the sleeve is at an abnormally high temperature, sparks are likely to occur obliquely from the electrode exposed portion at the tip of the insulating sleeve. In order to avoid this, it is necessary to position the insulating sleeve further on the inner side in the width direction of the melt, and as a result, it is impossible to perform close contact molding on the CR at the end of the film-like melt, resulting in unstable width fluctuations. This is a serious problem that causes uneven stretching at the end of the film product in the subsequent biaxial stretching step.

  It is an object of the present invention to enable heating and maintaining an electrode at a high temperature, to prevent the adhesion of an electrode with a low molecular weight, and to obtain long-term discharge stability and easy discharge characteristics. An object of the present invention is to provide a method for industrially and stably producing a biaxially stretched plastic film having excellent quality by preventing a spark discharge trouble that occurs.

  The inventors of the present invention have completed the present invention as a result of intensive studies in order to solve such problems.

  That is, the present invention is a method for producing a plastic film using a cooling molding method in which a molten resin is extruded from a die into a film shape, and the film-like melt is brought into close contact with the surface of a rotary cooling roll using an electrostatic adhesion method. When the heater is heated by directly passing an electric current through an electrode installed in the width direction of the film-like melt in the vicinity of the rotary cooling roll in order to perform electro-adhesion, as the electrode, the melt end from the both-end support part In another aspect of the present invention, there is provided a method for producing a plastic film, comprising using an electrode having an electrical resistance lower than that of other portions up to an inner position in the melt width direction.

  The present invention also relates to an apparatus for producing a plastic film using means for bringing a film-like melt composed of a molten resin extruded from a die into close contact with the surface of a rotary cooling roll using an electrostatic contact method. An electrode for generating an electric charge for electro-adhesion is arranged in the width direction of the film-like melt in the vicinity of the rotating cooling roll, and a current is passed directly to the electrode to heat the heater. The plastic film manufacturing apparatus is characterized in that the electrical resistance is reduced more than other portions from the both end support portions to the inner position in the melt width direction from the melt end portions.

  Any means for reducing the electrical resistance can be employed. According to the present invention, as a means for reducing the electrical resistance, it is particularly desirable to provide a splint electrode that substantially enlarges the cross-sectional area of the electrode. In addition, for example, a method of making the cross-sectional area of both ends of the electrode itself larger than that of other portions can be employed. Further, for example, a method of changing the material of both ends of the electrode to a material having higher electric conductivity than other portions can be employed.

  According to the present invention, the electrode is always used by using an electrode whose electrical resistance is lower than that of the other part from the both end support part to the position inside the melt width direction from the melt end part. It is possible to maintain heating at a high temperature, thereby obtaining stable discharge characteristics that do not change with time, and avoiding spark discharge troubles that occur at the ends of the electrodes. As a result, a biaxially stretched plastic film having excellent quality can be produced industrially and stably.

It is a front view of the principal part of the manufacturing apparatus of the plastic film of embodiment of this invention. It is a left view of the part shown by FIG.

Hereinafter, the present invention will be described in detail.
As shown in FIGS. 1 and 2, a film-like melt 2 is extruded from the T-die 1 onto the surface of the CR 3, and an electrostatic charge is imparted by the electrode 4 installed near the contact point where the melt 2 contacts the CR 3 to melt the melt. The body 2 is electrostatically adhered to the surface of CR3. The structure of the electrode 4 is that the electrode 4 is stretched between the left and right supports 5 and pulled, and the support 5 at both ends extends from the end of the melt 2 to the position inside the melt 2 in the width direction. A splint electrode 6 that substantially enlarges the cross-sectional area of the electrode is provided. Furthermore, insulating sleeves 7 are mounted outside the left and right ends of the film-like melt 2 so that the discharge width can be adjusted by sliding.

  As the splint electrode 6 that substantially enlarges the cross-sectional area in the present invention, for example, if the electrode 4 is a wire electrode, the cross-sectional shape along the wire is a circle, ellipse, semicircle, or crescent type metal. The thing which made the material contact or the thing which covered the tubular pipe | tube on the wire etc. are mentioned. If the electrode 4 is a blade-like electrode, it may be sandwiched between two plate-like metal materials or inserted into an oval tube, or the non-discharge side edge is inserted into a U-shaped bracket. . However, it is not limited to these.

  An important function of the splint electrode 6 in the present invention is to substantially expand the cross-sectional area of the electrode 4 so that when the electrode 4 is heated by direct heating, the heating current is also shunted to the splint side. (The apparent electrical resistance of the electrode 4 is lowered), and the self-heating per unit length of the electrode 4 itself provided with the splint electrode 6 can be suppressed. That is, even if this electrode portion is shielded by the insulating sleeve 7, a low temperature can be maintained without causing abnormal heat generation.

  Furthermore, by devising the shape of the splint electrode 6, it is possible to moderately suppress the discharge capability of the electrode end portion composed of the electrode 4 and the splint electrode 6.

  Regarding the discharge phenomenon, there is a proportional correlation between the radius of curvature of the discharge electrode and the discharge capacity in principle, and if the radius of curvature of the electrode 4 is increased by the splint electrode 6, the discharge current can be suppressed to a level just below that. . That is, the electrode end provided with the splint electrode 6 uses the synergistic effect of the low temperature maintenance effect and the discharge current suppression effect depending on the discharge tip shape, so that the tip of the insulating sleeve 7 is attached to the film-like melt 2. It is not necessary to put deeper into the inner side in the width direction of the melt 2 than the end portion of the melt. Thereby, it is possible to avoid the risk of sparking directly to CR2 while the end portion of the film-like melt 2 is also formed in close contact with CR2.

  Examples of the metal material used for the splint electrode 6 include a copper alloy, nickel, steel, stainless steel, tungsten, and an amorphous alloy. However, it is not limited to these. However, a material whose conductivity is significantly reduced by surface oxidation is not preferable.

  In the present invention, the temperature of the electrode 4 is preferably maintained at 350 ° C. or higher and lower than 400 ° C.

  In order to prevent electrode condensation of low molecular weight substances such as monomers and oligomers, it is preferable to heat at least 350 ° C. or higher, and in order to obtain low voltage and easy discharge characteristics, a higher temperature range is preferable, but 400 ° C. or higher. In this case, the oxidative deterioration of the metal becomes remarkable, and conversely the life of the electrode is shortened.

As the electrode temperature measuring method in the present invention, a metal resistance temperature measuring method can be used.
This is based on the principle that the resistivity changes depending on the temperature. The metal materials of the electrode 4 and the splint electrode 6 are previously placed in a furnace controlled to be heated to a high temperature, and the correlation between the temperature of 200 to 500 ° C. and the resistance value. The relationship is calibrated and the temperature coefficient of resistivity is measured. Next, the practical temperature can be calculated from the change in resistance value by accurately measuring the output voltage / current from the electrode heating power source. The temperature setting of the electrode 4 in the present invention can be performed by finely adjusting the output of the electrode heating power supply so that the calculated temperature reaches the target temperature.

  In the present invention, preferably, the cross-sectional area enlargement ratio of the electrode portion provided with the splint electrode 6 is 2 to 10 times that of the electrode 4, and the resistance value is 1 / 1.5-1 to 4.0. is there.

  The heater heating current of the electrode 4 is diverted to the side of the splint electrode 6 to suppress self-heating. However, if the heat generation is excessively suppressed, low molecular weight substances adhere to the splint electrode 6 or are exposed. This is not preferable because the adhesion of the melt 2 directly below 6 to the CR3 is remarkably lowered and the width of the film is changed. It is necessary to maintain a moderate temperature and a moderate low level discharge capability. These are determined by the conductive performance of the electrode 4 and the splint electrode 6, but the cross-sectional area enlargement ratio is 2 to 10 times and the resistance value is in the range of 1 / 1.5-1 to 4.0. These can be maintained well.

  As the electrode 4 used in the present invention, a wire having a wire diameter of 0.05 to 0.2 mm or a blade having a thickness of 0.01 to 0.05 mm is preferable because of its practical discharge capability.

  As CR3 used for this invention, what has the structure where a cooling medium (water) circulates inside, and made surface temperature 15-60 degreeC is preferable. Below 15 ° C, water droplets are condensed on the surface of CR3, causing adhesion of film-like melt 2 and film defects due to a water film, or sparking on the water droplets at the end of CR3 where film-like melt 2 is not in contact. It is not preferable because a trouble of discharging occurs. Moreover, when it exceeds 60 degreeC, since peeling from the surface of CR3 of a film will become difficult and a film will be extended | stretched to the vertical direction by peeling stress, a stretch spot will be caused at the following process.

  The surface material and surface finish of CR3 are not particularly limited.

  The plastic film referred to in the present invention is not particularly limited as long as it is a thermoplastic resin to which the electrostatic contact method can be applied.

  For example, a polyester film represented by polyethylene terephthalate, a polyolefin film such as polyethylene or polypropylene, a polyamide film such as nylon 6 or nylon 66, or a copolymer or a mixture containing these polymers. The present invention is extremely useful for forming an unstretched film for a polyester biaxially stretched film, which is particularly demanding for thickness accuracy and optical distortion.

  Hereinafter, the present invention will be described specifically by way of examples. However, the present invention is not limited to this.

[Example 1]
Molten polyethylene terephthalate was extruded into a film form from a T die, a cooling roll having a surface temperature of 20 ° C. was rotated at a speed of 60 m / min, and a non-oriented film having a width of 1100 mm and a thickness of 195 μm was cooled and molded by an electrostatic adhesion method.

  At this time, a tungsten wire having a diameter of 0.1 mm is installed near the contact point between the film-like melt and the cooling roll at a distance of 1450 mm between the supports, and from the support to the width direction of the melt rather than the end of the film-like melt. A splint electrode composed of a stainless steel tube covering the electrode was provided up to a position of 10 mm inside. The cross-sectional area enlargement ratio by the splint electrode was 6.2 times, and the conduction resistance was about 1/3. Further, an insulating ceramic sleeve was covered on both ends of the electrode, and the end of the sleeve was placed at a position about 3 mm inside the width direction of the melt from the end of the film-like melt. While applying a heating current to the electrode and maintaining the temperature of the electrode at 400 ° C., a DC positive voltage of 6.5 kV is applied to the electrode to give an electrostatic charge to the film-like melt, and the film is brought into close contact with the cooling roll. It was.

  Even after 48 hours from the start of production, no defects in appearance were observed in the unstretched film. The cooled molded film was biaxially stretched in the longitudinal and lateral directions at a stretching ratio of 4 times to obtain a biaxially stretched polyethylene terephthalate film having a thickness of 12 μm. A film excellent in thickness and optical uniformity was stably obtained.

[Comparative Example 1]
A polyethylene terephthalate film was cooled and molded under the same conditions as in Example 1 except that no splint electrode was provided.

  As a result, the portion shielded by the ceramic sleeve became red hot, causing oxidative deterioration in a short time and breaking. Therefore, it was unavoidable to directly reduce the heating current and bring the discharge electrode to 200 ° C.

  After 20 hours from the start of production, streamer discharge was intermittently generated, and surface roughness was observed on the unstretched film. This defect was also observed in the biaxially stretched film and was rejected as a film product.

[Example 2]
A polyethylene terephthalate film was cooled and molded under the same conditions as in Example 1 except for the following.

  That is, instead of the wire of Example 1, a stainless steel blade having a width of 3 mm and a thickness of 0.02 mm was installed near the contact point between the film-shaped melt and the cooling roll at a distance of 1450 mm between the supports. A splint electrode was provided by sandwiching the U-shaped metal fitting to the position 10 mm inside from the edge of the melt in the width direction of the melt. The cross-sectional area expansion ratio by the splint electrode was 6.2 times, and the conduction resistance was about 1/4. Furthermore, a ceramic sleeve was put on both ends of the electrode, and the tip of the sleeve was placed at a position about 3 mm inside the width direction of the melt from the end of the film-like melt. While applying a heating current to the electrode and maintaining the temperature of the electrode at 400 ° C., a DC positive voltage of 6.5 kV is applied to the electrode to give an electrostatic charge to the film-like melt, and the film is brought into close contact with the cooling roll. It was.

[Comparative Example 2]
A polyethylene terephthalate film was cooled and molded under the same conditions as in Example 2 except that the splint electrode was not provided.

  As a result, the portion shielded by the ceramic sleeve became red hot, causing oxidative deterioration in a short time and breaking. Therefore, it was unavoidable to directly reduce the heating current and bring the discharge electrode to 200 ° C.

  After 20 hours from the start of production, streamer discharge was intermittently generated, and surface roughness was observed on the unstretched film. This defect was also observed in the biaxially stretched film and was rejected as a film product.

1 T-die 2 Film-like melt 3 Casting roll (CR)
4 electrode 5 electrode support 6 splint electrode 7 insulating sleeve

Claims (12)

  A method for producing a plastic film using a cooling molding method in which a molten resin is extruded from a die into a film shape, and the film-like melt is brought into close contact with the surface of a rotary cooling roll using an electrostatic contact method. Therefore, when the heater is heated by passing a current directly to an electrode installed in the width direction of the film-like melt in the vicinity of the rotary cooling roll, the melt width is larger than the melt end than the end of the melt as the electrode. A method for producing a plastic film, comprising using an electrode having an electric resistance lower than that of other portions up to a position inside the direction. 2. The method for producing a plastic film according to claim 1 , wherein the temperature of the electrode is maintained at 350 ° C. or higher and lower than 400 ° C. 3. The plastic film according to claim 1 or 2, wherein the cross-sectional area of the electrode is substantially enlarged by the splint electrode from the both-end supporting part of the electrode to a position inside the melt width direction from the melt end part. Manufacturing method. The cross-sectional area enlargement ratio of the electrode portion provided with the splint electrode is set to 2 to 10 times that of the electrode portion not provided with the splint electrode, and the resistance value of the electrode portion provided with the splint electrode is not provided with the splint electrode 4. The method for producing a plastic film according to claim 3 , wherein the resistance value of the electrode portion is 1 / 1.5-1 / 4.   The method for producing a plastic film according to any one of claims 1 to 4, wherein a wire having a wire diameter of 0.05 to 0.2 mm is used as the electrode.   The method for producing a plastic film according to any one of claims 1 to 4, wherein a blade having a thickness of 0.01 to 0.05 mm is used as the electrode.   An apparatus for producing a plastic film using means for adhering a film-like melt composed of a molten resin extruded from a die to the surface of a rotary cooling roll using an electrostatic adhesion method, for electrostatic adhesion An electrode for generating an electric charge is installed in the width direction of the film-like melt in the vicinity of the rotary cooling roll, and the heater is heated by directly passing an electric current to the electrode. The plastic film manufacturing apparatus is characterized in that the electrical resistance is reduced as compared with other portions from the end of the melt to the position inside the melt width direction. 8. The plastic film manufacturing apparatus according to claim 7 , wherein the electrode is heated and maintained at 350 ° C. or higher and lower than 400 ° C. The splint electrode which substantially expands the cross-sectional area of an electrode from the both-ends support part of the electrode to the position inside the melt width direction from the melt end part is provided. Plastic film manufacturing equipment. The cross-sectional area enlargement ratio of the electrode portion provided with the splint electrode is 2 to 10 times that of the electrode portion not provided with the splint electrode, and the resistance value of the electrode portion provided with the splint electrode is provided with the splint electrode. 10. The apparatus for producing a plastic film according to claim 9 , wherein the resistance value of the non-electrode portion is 1 / 1.5 to 1 / 4.0.   The plastic film manufacturing apparatus according to any one of claims 7 to 10, wherein the electrode is a wire having a wire diameter of 0.05 to 0.2 mm.   11. The plastic film manufacturing apparatus according to claim 7, wherein the electrode is a blade having a thickness of 0.01 to 0.05 mm.

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