JP4352854B2 - Production apparatus and production method for polyester resin sheet - Google Patents

Description

The present invention produces a sheet having a uniform thickness and few surface defects by extruding a thermoplastic resin from an extruder into a sheet in a molten state, and bringing the molten sheet into close contact with a moving cooling body and cooling. A method for producing a polyester resin sheet is provided.

  Conventionally, in order to form a sheet having a uniform thickness and width by efficiently extruding a molten thermoplastic resin into a sheet form on a moving cooling body from a T die of an extruder, for example, Patent Document As shown in FIG. 1, by applying a high voltage to a wire-like or knife-edge-like electrode arranged along the moving cooling body, an electrostatic charge is applied to the molten sheet-like body, thereby being in close contact with the moving cooling body Has been done. When the molten sheet-like body is electrostatically brought into close contact with the moving cooling body using the wire-like or knife-edge-like electrode in this way, the moving speed of the molten sheet-like body and the moving cooling body is 25 m / min. By setting the speed relatively low, it is possible to efficiently cool the moving cooling body by properly bringing the molten sheet into close contact with the moving cooling body.

  In addition, for example, as disclosed in Patent Document 2, a needle-like, saw-shaped, saw, etc., can be efficiently cooled by properly adhering a molten sheet-like body to a moving cooling body that moves at a relatively high speed of about 40 m / min. A streamer corona discharge is applied to the molten sheet from the blade-shaped, wire-shaped, or knife-edge electrode to apply a large amount of electric charge, so that the molten sheet is electrostatically adhered to the moving cooling body. It has been broken.

Furthermore, as shown in Patent Document 3, for example, the melt specific resistance of the thermoplastic resin constituting the molten sheet-like body by including at least one of an alkali metal, an alkaline earth metal, or a compound thereof in the polyester resin, etc. Is set to a low value, the moving speed of the moving cooling body when the molten sheet-like body is cooled by electrostatically bringing the molten sheet-like body into close contact with the moving cooling body by applying a high voltage to the electrodes. It is known that the speed can be increased.
Japanese Examined Patent Publication No. 37-6142 JP-A-56-105930 Japanese Patent Publication No.53-40231

  In the electrostatic contact method using the wire-shaped or knife-edge-shaped electrode disclosed in Patent Document 1, when the moving speed of the molten sheet-shaped body and the moving cooling body is increased to 25 m / min or more, the moving cooling body Due to the presence of the air film formed according to the accompanying flow generated on the surface, the adhesion of the molten sheet-like body to the moving cooling body becomes insufficient, and the cooling action of the molten sheet-like body by the moving cooling body is impaired. It will be. As a result, before the molten sheet is sufficiently cooled, its crystallization progresses and the transparency is lowered, and bubbles or streaks are easily generated on the surface of the sheet, and the molten sheet is There is a problem that the thickness of the sheet tends to be non-uniform due to not being uniformly cooled.

In the streamer corona discharge-type electrostatic contact method disclosed in Patent Document 2, the molten sheet-like body can be brought into close contact with the moving cooling body and efficiently cooled. For example, polyethylene terephthalate having a melt specific resistance of about 0.4 × 10 ⁸ (Ω · cm) is not limited to polyamide resin of 0 × 10 ⁶ (Ω · cm) or less. Was supposed to be unable to do. Therefore, a resin material having a high melting resistivity such as polyethylene terephthalate is not used as a raw material of a sheet that is electrostatically adhered to a moving cooling body by streamer corona discharge, and has a low melting resistivity such as a polyamide resin. Only was used.

  Furthermore, as shown in the above-mentioned Patent Document 3, by adding an additive such as an alkali metal into the thermoplastic resin that is the raw material of the sheet to lower the melting specific resistance value of the molten sheet, The moving sheet and the moving cooling body are configured to be efficiently cooled by bringing the molten sheet-like body into intimate contact with the moving cooling body by increasing the moving speed of the moving body and the moving cooling body and ensuring the adhesion between the molten sheet-like body and the moving cooling body. In such a case, there has been a problem that in order to reduce the melting specific resistance value of the molten sheet-like material, the non-foreign material property, color tone, heat resistance and the like inherent in the raw material must be sacrificed to some extent.

  Further, as disclosed in Patent Documents 2 and 3, when a thermoplastic resin having a low melting specific resistance value is used as a raw material for the sheet, the current flowing from the electrode to the moving cooling body becomes too large, and a spark is generated. Since the discharge tends to easily occur, it is necessary to prevent the occurrence of the spark discharge by, for example, installing an electrode upstream of the contact point of the molten sheet-like body with the moving cooling body. In this way, when the electrode is installed on the upstream side of the contact point of the molten sheet-like body with respect to the moving cooling body, the molten sheet-like body vibrates and is easily damaged by contact with the electrode in order to prevent this. For this, it is necessary to separate the molten sheet-like body and the electrode to some extent. When the electrodes are thus separated from the molten sheet-like body, there is a problem that the streamer corona discharge cannot be stably generated unless the voltage applied between the electrodes is set high.

The present invention has been made in view of the above points, and provides a method for producing a polyester-based resin sheet capable of appropriately producing a sheet at high speed without deteriorating the inherent properties of raw materials. is there.

The invention according to claim 1 is an extrusion process in which a polyester resin having a melt specific resistance value of 0.3 × 10 ⁸ (Ω · cm) or more is extruded from the extruder as a molten state, and extruded from the extruder. In the method for producing a polyester resin sheet, comprising a cooling step of cooling the molten sheet-like body in close contact with the moving cooling body and a stretching step of stretching the cooled sheet-like body, a plurality of needle-like electrodes are melted A tapered shape in which a sphere having a radius of 0.01 mm to 0.05 mm is inscribed at the tip of the needle electrode and is inscribed in the peripheral surface of the most distal portion, arranged at a constant interval in a direction perpendicular to the sheet-form conveying direction. And the gap between the acicular electrode and the molten sheet is set within a range of 0.5 mm to 5 mm, and the interval between the acicular electrodes is set to the acicular electrode and the molten sheet Less than 5 times the gap between By performing streamer corona discharge on the molten sheet-like body in the cooling step from the corona discharge portion set to, the molten sheet-like body is brought into close contact with the moving cooling body and cooled.

The invention according to claim 2 is the method for manufacturing a polyester resin sheet of the sheet according to claim 1 , wherein the apex angle of the tapered portion provided at the tip of the needle electrode is set to less than 90 °. Is.

According to the first aspect of the present invention, by applying a predetermined voltage between each needle electrode and the moving cooling body to perform streamer corona discharge in which a large current flows through the molten sheet body, 0.3 × Since a large amount of electric charge can be stably and continuously applied to a molten sheet-like body made of a thermoplastic resin having a melt specific resistance value of 10 ⁸ (Ω · cm) or more, the above-mentioned molten sheet-like body and moving cooling body Even when the moving speed is set at a high speed, the molten sheet-like body can be properly brought into close contact with the moving cooling body and cooled uniformly. Therefore, by mixing a predetermined additive into the thermoplastic resin that is the raw material of the sheet, it is uniform without causing problems such as non-foreign material property, color tone or heat resistance inherent in the raw material. There is an advantage that a sheet having a large thickness and having no surface defects can be produced efficiently at high speed.

According to the invention according to claim 2 , without making the gap between the needle-like electrode and the molten sheet-like body unnecessarily small, the concentration of the electric field at the tip of the needle-like electrode can be effectively increased, There is an advantage that stable streamer corona discharge can be performed from the tip of the needle electrode to the molten sheet.

FIG. 1 shows a specific example of a production apparatus used for carrying out the method for producing a polyester resin sheet according to the present invention. The manufacturing apparatus includes an extruder 3 that extrudes a thermoplastic resin material supplied from a hopper 1 into a sheet form from a die 2 made of a T-die or the like in a molten state by kneading the thermoplastic resin material, and a melt extruded from the extruder 3. A moving cooling body 5 composed of a cooling roller or the like for cooling the sheet-like body 4a, and a corona discharge portion 6 for bringing the molten sheet-like body 4a into close contact with the moving cooling body 5 by performing a streamer corona discharge on the molten sheet-like body 4a. The first stretched portion 7 for stretching the sheet-like body 4b cooled by the moving cooling body 5 in the longitudinal direction, the second stretched portion 8 for stretching the sheet-like body 4b in the width direction, and the stretched sheet 4c And a winding unit 9 for winding the wire.

  As shown in FIGS. 2 and 3, the corona discharge unit 6 includes a plurality of facing the surface of the molten sheet 4 a in the vicinity of the contact point Z of the molten sheet 4 a with the peripheral surface of the moving cooling body 5. Needle electrode 10 is provided. These needle-like electrodes 10 are arranged at a constant interval W in a direction perpendicular to the conveying direction of the molten sheet-like body 4a, and the axis of the needle-like electrode 10 is perpendicular to the surface of the molten sheet-like body 4a. Is installed.

  The needle electrode 10 is formed in a columnar shape with iron, brass, stainless steel, tungsten, or the like having a diameter of 1 mm or less, preferably 0.5 mm or less, and each needle electrode 10 and the molten sheet-like body 4a A predetermined gap N is provided between them. Then, a predetermined voltage is applied between the acicular electrode 10 and the moving cooling body 5 from the DC high-voltage power source 11, and streamer corona discharge from the acicular electrode 10 to the molten sheet-like body 4 a on the moving cooling body 5. As a result, a large amount of electric charge is continuously applied so that the molten sheet-like body 4a is in electrostatic contact with the moving cooling body 5.

  The streamer corona discharge refers to a state in which, for example, the needle-like electrode 10 to which a positive voltage is applied and the molten sheet-like body 4a that is a ground body are bridged to perform stable corona discharge. That is, when the voltage applied between the needle-like electrode 10 and the moving cooling body 5 is increased, a dark current state (non-sustainable discharge phenomenon) occurs first, and then a glow corona discharge state occurs. Next, a streamer corona discharge state in which air is ionized by the discharge from the needle electrode 10 and a stable current continuously flows is obtained. When the voltage is further increased from this state, a spark discharge state is obtained.

  Looking at each discharge phenomenon in terms of the relationship between voltage and current, in the dark current region, the minute current region where Ohm's law is established, that is, the region where current flows in proportion to the voltage, and even if the voltage is increased, the current does not increase. There is a region, and when the voltage is further increased from this region, the current rapidly increases, and this region is a glow corona discharge region, and purple light emission covering the surface of the electrode is observed. When the voltage is further increased from this glow corona discharge region, a streamer corona discharge state is established, and at this time, light emission bridging the electrode and the earth body is observed. When the relationship between the voltage V (kV) applied to the electrode and the current value I (mA / cm) corresponding to the width dimension of the sheet-like body that is the ground body is specifically seen, I <0.025 × V A region where −0.12 is a dark current region or a glow corona discharge region, and a region where I ≧ 0.025 × V−0.12 is a streamer corona discharge region.

  As described above, streamer corona discharge is performed from each acicular electrode 10 of the corona discharge portion 6 to the molten sheet-like body 4a extruded from the extruder 3 onto the moving cooling body 5, and a large amount of charge is melted. By being applied to the sheet-like body 4 a, the molten sheet-like body 4 a becomes in a state of being in electrostatic close contact with the moving cooling body 5, and heat is generated between a cooling medium such as cooling water supplied to the moving cooling body 5. The melted sheet-like body 4a is cooled by exchange.

  When the gap N between the needle-like electrode 10 and the molten sheet-like body 4a, that is, the distance between the tip surface of the needle-like electrode 10 and the surface of the molten sheet-like body 4a located on the moving cooling body 5 is less than a certain value. The tip of the needle-like electrode 10 may come into contact with the molten sheet 4a and the molten sheet 4a may be damaged. When the distance exceeds a certain value, it is applied to properly perform streamer corona discharge. It is inevitable that spark discharge is likely to occur due to the necessity of extremely high voltage. For this reason, the gap N between the needle-like electrode 10 and the molten sheet-like body 4a is set within a range of 0.5 mm to 5 mm, and a preferable range thereof is 1 mm to 4 mm.

  When the installation interval W of the needle-like electrodes 10 arranged in the direction orthogonal to the conveying direction of the molten sheet-like body 4a, that is, the distance between the axial centers of the adjacent needle-like electrodes 10 becomes a certain value or more, A discharge interval from the electrode 10 to the molten sheet-like body 4a becomes too wide, and a streak-like poor adhesion portion is easily generated therebetween. In order to prevent such adverse effects, the installation interval W is set to be less than 5 times the gap N between the needle electrode 10 and the molten sheet-like body 4a. Further, when the interval W between the needle electrodes 10 is equal to the diameter of the needle electrodes 10, the adjacent needle electrodes 10 cannot contact each other as shown in FIG. Therefore, the lower limit value of the installation interval W is a value corresponding to the diameter of the needle electrode 10. A preferable range of the installation interval W is within a range of 1 to 3 times the gap N between the needle-like electrode 10 and the molten sheet-like body 4a. When the gap N with the body 4a is 1 mm, the preferable range of the installation interval W is 1 mm to 3 mm.

  As shown in FIG. 5, a conical tapered portion 10 a in which a sphere Q having a predetermined radius r is inscribed in the most peripheral surface is formed at the tip of the needle electrode 10. In order to increase the concentration of charges at the tip of the needle electrode 10 and efficiently generate streamer corona discharge, the radius r of the sphere Q inscribed in the peripheral surface of the tip of the tapered portion 10a is set to 0. However, if the radius of the sphere Q is excessively small, it becomes difficult to form the tapered portion 10a, and the tip of the needle electrode 10 is easily damaged during handling. Become. Therefore, a preferable range of the radius r is 0.005 mm to 0.09 mm, and a more preferable range is 0.01 mm to 0.05 mm. The radius r of the sphere Q is obtained by drawing a circle inscribed on the peripheral surface of the most distal portion of the needle electrode 10 and measuring the radius.

When the adhesion force F [Pa] of the molten sheet-like body 4a to the moving cooling body 5 is considered as a clonal force, it is expressed as the following formula. In the following equation, q is the charge [C] on the sheet, E is the electric field [V / m] of the sheet, and S is the sheet area [cm 2 defined by the length and width of the sheet moving per unit time (1 s). ], I is the current [A] flowing through the electrostatic contact electrode, V is the voltage [V] applied to the electrode, v is the moving speed [m / s] of the moving cooling body 5, and w is cooled by electrostatic contact. The sheet width [m], k is the electric field concentration degree [1 / m] defined by the equation k = E / V, and is obtained by analytical calculation in the case of a simple shape, and in the case of a complicated shape. Is obtained by numerical calculation using the finite element method.

F [Pa] = q [C] × E [V / m] / S [cm ² ]
= I · V · k / (v · w) [Pa]
From the above formula, the electrostatic adhesion force of the molten sheet 4a with respect to the moving cooling body 5 is determined according to the applied voltage V, current i, and electric field concentration k to the electrode. It can be seen that the electroadhesion force F can be increased.

  In order to prevent the gap N with the molten sheet-like body 4a from becoming less than a certain value and further increase the concentration of charges at the tip of the needle-like electrode 10 to increase the electrostatic adhesion force. Therefore, it is desired to make the apex angle θ of the tapered portion 10a as small as possible, and it is preferable to set the apex angle θ to less than 90 °. When the apex angle θ is 90 ° or more, the radius r of the sphere Q inscribed in the peripheral surface of the tip of the tapered portion 10a is set to about 0.04 mm, and the needle electrode 10 and the molten sheet-like body This is because stable streamer corona discharge cannot be performed unless the gap N with respect to 4a is 1.5 mm or less. In addition, if the apex angle θ of the tapered portion 10a becomes too small, it is difficult to set the radius r of the sphere Q inscribed in the peripheral surface of the most distal portion of the tapered portion 10a within the preferable range. The preferred angle of the apex angle θ is around 30 °.

  Further, a difference in height occurs between the needle-like electrodes 10 arranged in the direction orthogonal to the conveying direction of the molten sheet-like body 4a, and the gap is formed between the molten sheet-like body 4a and each needle-like electrode 10. When the gap N varies, a discharge spot is generated, and a poor adhesion portion is easily formed. When the applied voltage is increased to prevent this, partial whitening phenomenon is likely to occur in the molten sheet-like body 4a. When this whitening phenomenon occurs, defects such as surface roughness of the sheet can be found by inspection. Therefore, the height difference between the needle-like electrodes 10, that is, the variation in the protrusion length of each needle-like electrode 10 with respect to the moving cooling body 5 is set to less than 0.3 mm, preferably less than 0.2 mm. It is configured to prevent the gap N between the needle-like body 4a and each needle-like electrode 10 from becoming uneven as much as possible.

The thermoplastic resin that is heat-kneaded and extruded by the extruder 3 is not particularly limited as long as the melt specific resistance value R is 0.3 × 10 ⁸ (Ω · cm) or more. Resin is envisioned. The melting specific resistance value R is determined by placing the thermoplastic resin in a vacuum after drying it in a test tube having a diameter of 50 mm, melting it in a nitrogen atmosphere, and then in the thermoplastic resin in a nitrogen atmosphere at 285 ° C. A pair of copper electrodes are inserted, and the equation R = (V · S / I) according to the current value and the voltage value, the electrode area, and the distance between the electrodes measured with a voltage applied to the both electrodes from the DC high voltage generator. * Calculated based on L). In this equation, V is a voltage value, S is an electrode area, I is a current value, and L is a distance between electrodes.

  Examples of the thermoplastic resin having a high melting specific resistance value include, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, or a polyester resin composed of a copolymer mainly composed of a polymer component constituting these resins. Are preferably used.

  When the above copolymer is used, the dicarboxylic acid component includes aliphatic dicarboxylic acids such as adipic acid, sebacic acid, dodecanedioic acid; terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,2-bis And aromatic dicarboxylic acids such as phenoxyethane-p, p′-dicarboxylic acid; and ester-forming derivatives thereof (2,5-dimethylterephthalic acid and the like). Polyfunctional carboxylic acids such as trimellitic acid and pyromellitic acid may be used.

  The glycol component of the copolymer includes ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,3 propanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, trimethylolpropane. , P-xylene glycol or the like, or polyethylene glycol having an average molecular weight of 150 to 2000 is used.

  In addition, you may make the composition of the said polyester-type resin contain various well-known additives which consist of an antistatic agent, UV absorber, or a stabilizer, for example.

Also, instead of the polyester resin having a high melting specific resistance value, by mixing a material having a low melting specific resistance value and various additives (for example, a resin having a high melting specific resistance value), the melting specific resistance value is obtained. May be adjusted to 0.3 × 10 ⁸ (Ω · cm) or more.

As the thermoplastic resin heated and kneaded by the extruder 3, polyethylene terephthalate having a melt specific resistance value of 0.3 × 10 ⁸ (Ω · cm) or more is used, and the sheet is formed using the manufacturing apparatus having the above configuration. The manufacturing method of the sheet to manufacture is demonstrated below. First, polyethylene terephthalate pellets blended with particles for imparting slipperiness as required are sufficiently dried in vacuum, and then supplied to the hopper 1 of the extruder 3 and heated and kneaded, whereby a die is formed. For example, a molten sheet-like body 4 a having a temperature of about 280 ° C. and a thickness of about 200 μm is extruded from 2 and brought into contact with the peripheral surface of the moving cooling body 5.

  A positive voltage is applied to the needle-like electrode 10 disposed along the vicinity of the contact point Z between the molten sheet-like body 4a extruded onto the moving cooling body 5 and the moving cooling body 5 as described above, By generating streamer corona discharge in the molten sheet-like body 4a, a large amount of electric charge is continuously given to the molten sheet-like body 4a, and the molten sheet-like body 4a is conveyed at a predetermined speed while the moving cooling body 5 It is cooled by electrostatic contact with the peripheral surface.

  That is, a plurality of needle-like electrodes 10 are arranged at regular intervals in a direction orthogonal to the conveying direction of the molten sheet-like body 4a, and the installation interval W of each needle-like electrode 10 is set to the needle-like electrode 10 and the molten sheet-like body 4a. In the state where the gap N between the acicular electrode 10 and the molten sheet 4a is set within a range of 0.5 mm to 5 mm, the acicular electrode 10 A high DC voltage is applied between the movable cooling body 5 and the moving cooling body 5. As a result, streamer corona discharge is performed on the molten sheet 4a, so that a large amount of charge is applied to the molten sheet 4 and the molten sheet 4 is charged. Thus, the molten sheet-like body 4a is brought into electrostatic contact and is effectively cooled.

  The sheet-like body 4b cooled by the moving cooling body 5 is supplied to the first extending portion 7 and extended in the longitudinal direction of the sheet-like body 4b, and then supplied to the second extending portion 8 to supply the sheet-like body 4b. By stretching in the width direction, a sheet 4 c having a predetermined width dimension and thickness is manufactured, and the sheet 4 c is wound up in a roll shape at the winding unit 9.

Thus, an extruder 3 for extruding a polyester resin having a melting specific resistance value of 0.3 × 10 ⁸ (Ω · cm) or more into a sheet in a molten state, and a molten sheet-like body extruded from the extruder 3 Manufacturing apparatus provided with moving cooling body 5 for cooling 4a and corona discharge section 6 for causing molten sheet-like body 4a to adhere electrostatically to moving cooling body 5 by performing streamer corona discharge on molten sheet-like body 4a In the method for producing a polyester resin sheet using a plurality of needle-like electrodes 10, a plurality of needle-like electrodes 10 are arranged in the corona discharge part 6 at a constant interval in a direction perpendicular to the conveying direction of the molten sheet-like body 4 a. The gap N between the molten sheet-like body 4a is set within a range of 0.5 mm to 5 mm, and the installation interval W of each needle-like electrode 10 is set to the gap N between the needle-like electrode 10 and the molten sheet-like body 4a. Since it is set to less than double, a sheet having a uniform thickness and having no surface defects can be efficiently produced at high speed without causing problems such as non-foreign substances, color tone or heat resistance inherent in the raw material. There is an advantage.

  That is, since the gap N between the needle electrode 10 and the molten sheet 4a is set in the range of 0.5 mm to 5 mm, a streamer that allows a large current to flow through the molten sheet 4a without excessively increasing the applied voltage. By performing corona discharge, a large amount of charge can be imparted to the molten sheet-like body 4 a and the molten sheet-like body 4 a can be electrostatically adhered to the peripheral surface of the moving cooling body 5. Therefore, even when the moving speed of the molten sheet-like body 4a and the moving cooling body 5 is set to a high speed of, for example, 60 m / min or more, the molten sheet-like body is properly brought into close contact with the moving cooling body 5 and is cooled evenly. Thus, the productivity of the sheet can be improved without causing adverse effects such as roughening the surface of the sheet and lowering the transparency.

Further, by using the needle electrode 10 having the above-described configuration, it becomes possible to manufacture a sheet using a thermoplastic resin having a melting specific resistance value of 0.3 × 10 ⁸ (Ω · cm) or more as a raw material. Since it is not necessary to reduce the melting specific resistance value by adding an alkali metal or the like to the raw material, a sheet having excellent characteristics can be efficiently produced without impairing the non-foreign material property, color tone or heat resistance inherent in the raw material. There is an advantage that it can be manufactured well.

Moreover, by using a thermoplastic resin having a melting specific resistance value of 0.3 × 10 ⁸ (Ω · cm) or more as a raw material as described above, the contact point of the molten sheet-like body 4a with the moving cooling body 5 Even when the needle-like electrode 10 is disposed at a position close to Z, it is possible to prevent a situation in which a spark discharge occurs due to an excessively large current flowing from the needle-like electrode 10 to the moving cooling body 5. Accordingly, by disposing the needle-like electrode 10 at a position close to the contact point Z where the molten sheet-like body 4a is in close contact with the moving cooling body 5 and hardly vibrates, vibration of the molten sheet-like body 4a is prevented. As a result, it is possible to prevent occurrence of a situation in which the molten sheet-like body 4a contacts the needle-like electrode 10.

  Furthermore, by bringing the tip of each needle electrode 10 close to the molten sheet 4a as described above, the streamer corona discharge to the molten sheet 4a is appropriately generated at a low voltage, and the molten sheet 4a is Since the sheet can be electrostatically adhered to the moving cooling body 5, the surface of the sheet becomes rough and opaque, or air is partially trapped between the molten sheet-like body 4 a and the moving cooling body 5. Thus, there is an advantage that the molten sheet-like body 4a can be effectively cooled without causing any adverse effects such as formation of bubble-like or streak-like defects on the surface of the sheet.

  And as mentioned above, by setting the interval W between the needle-like electrodes 10 to be less than 5 times the gap N between the needle-like electrode 10 and the molten sheet-like body 4a, between the needle-like electrodes 10 adjacent to each other. Since the interval W is configured to be equal to or less than a predetermined value, it is possible to prevent the adjacent discharge interval from being increased when streamer discharge is performed from each needle electrode 10 to the molten sheet-like body 4a, and uniform streamer discharge is performed. Can be generated. For this reason, it is possible to effectively prevent a phenomenon in which a portion having high adhesion and a portion having low adhesion to the moving cooling body 5 are alternately generated, that is, a streak-like poor adhesion portion, and the entire molten sheet-like body 4a. There is an advantage that can be cooled uniformly.

  Moreover, in the said embodiment, since the spherical part which has a radius of less than 0.1 mm in the front-end | tip part provided in the front-end | tip part of the acicular electrode 10 the tapered part 10a which inscribed in the front-end | tip part peripheral surface, By effectively increasing the concentration of the electric field at the tip of 10, stable streamer corona discharge can be performed from the tip of the needle electrode 10 to the molten sheet 4 a. Therefore, without setting the voltage applied between the needle-like electrode 10 and the moving cooling body 5 to an excessively high value, a large amount of electric charge is continuously applied to the molten sheet-like body 4a to move the cooling. There is an advantage that the molten sheet-like body 4a is properly adhered to the body 5 so that the entire molten sheet-like body 4a can be uniformly cooled.

  Furthermore, as shown in the above embodiment, when the apex angle θ of the tapered portion 10 of the needle electrode 10 is set to less than 90 ° C., the concentration of the electric field at the tip of the needle electrode 10 is Since it can be increased more effectively, a streamer that is stable from the tip of the needle-like electrode 10 to the molten sheet-like body 4a without making the gap N between the needle-like electrode 10 and the molten sheet-like body 4a unnecessarily small. There is an advantage that the cooling performance can be effectively improved by performing corona discharge to bring the molten sheet-like body 4a into close contact with the moving cooling body 5.

  Further, as shown in the above embodiment, when the height difference of each needle electrode 10 is set to less than 0.3 mm, the melting in the direction orthogonal to the conveying direction of the molten sheet-like body 4a according to the height difference. It is possible to effectively prevent the occurrence of discharge spots due to variations in the gap N between the sheet-like body 4a and each needle-like electrode 10. Therefore, the partial whitening phenomenon occurs in the molten sheet 4a by suppressing the occurrence of poor adhesion of the molten sheet 4a to the moving cooling body 5 without increasing the applied voltage so much. The molten sheet-like body 4a can be efficiently cooled by properly adhering the molten sheet-like body 4a to the moving cooling body 5 while effectively preventing the above.

  Furthermore, in the above embodiment, since each needle electrode 10 is disposed in the vicinity of the contact point Z of the molten sheet 4a with respect to the moving cooling body 5, the surface of the sheet is roughened, or a hole is formed in the sheet. There is an advantage that the molten sheet-like body 4a can be effectively cooled by properly bringing the molten sheet-like body 4a into close contact with the moving cooling body 5 without causing any adverse effects such as.

  That is, the installation position of each needle electrode 10 is shifted by a certain value or more (for example, 5 mm or more) upstream of the contact point Z of the molten sheet 4a with the moving cooling body 5 in the conveying direction of the molten sheet 4a. The molten sheet is configured to generate a stable streamer corona discharge in the molten sheet-like body 4a in the vicinity of the contact point Z, so that the applied voltage is not set to an excessively high value. The sheet-like body 4a can be properly adhered to the moving cooling body 5 and the molten sheet-like body 4a can be appropriately cooled to effectively prevent the surface of the sheet from being roughened, and spark discharge can be prevented. There is an advantage that it is possible to effectively prevent the occurrence of the occurrence of a hole in the sheet.

  In addition, the installation position of each needle electrode 10 is a certain value or more (for example, 5 mm or more) on the downstream side in the conveying direction of the molten sheet 4a with respect to the contact point Z of the molten sheet 4a with respect to the moving cooling body 5. By preventing the shift and preventing the cooling and solidification from proceeding before the molten sheet 4a comes into close contact with the moving cooling body 5, the molten sheet 4a can be properly adhered to the moving cooling body 5. It is possible to suppress the partial trapping of air between the two, and this has the advantage that defects can be effectively prevented from forming in the form of bubbles or streaks on the surface of the sheet. In order to more effectively prevent the above adverse effects, the displacement amount of the installation position of each needle electrode 10 in the upstream direction or the downstream direction in the conveying direction of the molten sheet 4a with respect to the contact point Z is 3 mm or less. Is desirable.

Further, as described above, an extrusion process in which a thermoplastic resin having a melt specific resistance value of 0.3 × 10 ⁸ (Ω · cm) or more is extruded from the extruder 3 in a molten state, and extruded from the extruder 3. The molten sheet-like body 4a is brought into close contact with the moving cooling body 5 and cooled, and a stretching step for stretching the cooled sheet-like body is provided, and the plurality of needle-like electrodes 10 convey the molten sheet-like body 4a. The gap N between the needle-like electrode 10 and the molten sheet-like body 4a is set within a range of 0.5 mm to 5 mm, and the interval between the needle-like electrodes 10 is set. By performing streamer corona discharge on the molten sheet-like body 4a from the corona discharge portion 6 where W is set to be less than 5 times the gap N between the needle-like electrode 10 and the molten sheet-like body 4a, Close body 4a to moving cooling body 5 According to the method for manufacturing a sheet that is attached and cooled, the molten sheet 4a is appropriately attached to the moving cooling body 5 while the moving speed of the molten sheet 4a and the moving cooling body 5 is set to be high. There is an advantage that a sheet having a uniform thickness and having no surface defects can be efficiently produced at high speed by being able to cool evenly by close contact.

  In the above embodiment, the sheet manufacturing apparatus and the manufacturing method for extending the sheet-like body 4b in the two directions of the longitudinal direction and the width direction of the sheet by the first extending portion 7 and the second extending portion 8 after cooling have been described. The film may be stretched only in either one of the two directions. In the case of unidirectional stretching, a sheet having a thickness of 10 μm or more is preferably used because of its mechanical rigidity, and in the case of bi-directional stretching, a sheet of 2 μm or more is preferably used. Moreover, it is good also as a structure which provided the extending | stretching part which extends the sheet-like body 4b further to a longitudinal direction and the width direction in the downstream part of 7 and 8 of the said 1st, 2nd extending part.

  Further, instead of the above-described embodiment in which the conical tapered portion 10 is formed at the tip of the cylindrical needle-like electrode 10, the tip of the prismatic electrode has a pyramid shape as shown in FIG. The tapered portion 10a may be formed, and a spherical portion 10b in which a sphere having a predetermined diameter is inscribed may be provided at the most distal end portion.

In Examples 1a to 1c of the present invention, resin specific pellets containing CaCO _{3 in} polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g and resin pellets not containing CaCO ₃ were mixed to obtain a total melt specific resistance. A raw material having a value of 1.2 × 10 ⁸ (Ω · cm) was used, and this was dried under reduced pressure (1.3 hPa) at a temperature of 135 ° C. for about 6 hours, and then supplied to the extruder 3. The mixture was heated and kneaded at a temperature of 280 ° C., and extruded from the die 2 of the extruder 3 having a width dimension of 450 mm onto the moving cooling body 5 as a molten sheet-like body 4a.

  In addition, the electrodes 10 made of a plurality of brass needles are arranged at an installation interval W of 1 mm so as to face the peripheral surface of the moving cooling body 5 made of a metal roll whose surface temperature is kept at 20 ° C. With a gap N between the electrode 10 and the molten sheet 4a set to 1 mm, a voltage of about 3.0 kV is applied between the needle electrode 10 and the moving cooling body 5 to about 3.0 mA. The molten sheet-like body 4a having a width of 260 mm and a thickness of 140 μm is formed while moving the moving speed of the moving cooling body 5 at a speed of 80 m / min, 90 m / min, and 100 m / min. In addition, as a result of observing the adhesion state of the molten sheet-like body 4a to the moving cooling body 5, data as shown in Table 1 below was obtained.

  As the needle-like electrode 10 in each of the above Examples 1a to 1c, the diameter is set to 1 mm, and the apex angle θ of the tapered portion 10a provided at the tip is set to 30 °, and the needle-like electrode 10 By setting the gap N between the electrode 10 and the molten sheet-like body 4a to 1 mm, an A-type electrode in which the adjacent needle-like electrodes 10 contact each other as shown in FIG. 4 was used. Further, the radius r of the sphere Q inscribed in the most distal portion of the needle electrode 10 was set to 0.04 mm, and the height difference of the tip portion of each needle electrode 10 was set to less than 0.2 mm.

  On the other hand, in Comparative Examples 1a to 1c, an electrode made of a tungsten wire having a diameter of 30 μm is installed in the vicinity of the contact point Z of the molten sheet-like body 4a with respect to the peripheral surface of the moving cooling body 5 in place of the needle-like electrode 10. In addition, the gap between the electrode and the molten sheet-like body 4a is set to 5 mm, and the moving speed of the moving cooling body 5 is set to 30 m / min to 35 m / min. The voltage value and current applied during the period were adjusted to various values. Further, Comparative Examples 2a to 2c were configured in the same manner as Comparative Examples 1a to 1c except that a tape electrode having a thickness of 20 μm was installed instead of the tungsten wire.

  From the above data, in any of Example 1a of the present invention in which the moving speed of the moving cooling body 5 is set to 80 m / min, Example 1b set to 90 m / min, and Examples 1a to 1c set to 100 m / min. In addition, it is observed that streamer corona discharge is generated at intervals of 3 mm between the needle-like electrode 10 and the molten sheet-like body 4a, and the molten sheet-like body 4a is in close contact with the moving cooling body 5 in an appropriate state. confirmed. In Table 1, SC indicates that a streamer corona discharge phenomenon was observed, and a circle indicates that the entire molten sheet-like body 4a is completely cooled, and pin-like bubbles are formed on the surface of the sheet. This shows a state where no defects are observed. In Table 1, Δ marks indicate a state in which thin pin-shaped defects are partially recognized on the surface of the sheet, and X marks indicate pin-shaped defects or streak defects on the entire sheet. Shows the state.

  On the other hand, in the comparative examples 1a to 1c using the electrodes made of tungsten wires or the comparative examples 2a to 2c using the tape electrodes, if the moving speed of the moving cooling body 5 is faster than 30 m / min, the moving cooling Air bubbles or streaky spots were unavoidable between the body 5 and the molten sheet-like body 4a. In order to prevent this, when the applied voltage is increased, spark discharge (spark) occurs, the wire is cut, a cooling band is formed on the sheet, or the molten sheet-like body is wound around the moving cooling body 5. The sheet could not be properly manufactured.

  Example 2a of the present invention configured in the same manner as Examples 1a to 1c except that the apex angle of the needle electrode 10 is set to 90 ° and the interval W between the needle electrodes 10 is set to 2 mm. The interval W between the needle-like electrodes 10 is set to 2 mm, and the adjacent needle-like electrodes 10 are separated from each other as shown in FIG. 3, and the needle-like electrode 10 and the molten sheet-like body 4a are formed. Except for the point that the gap N is set to 2 mm, the apex angle of the needle electrode 10 is set to 90 °, and the apex angle of the needle electrode 10 is set as in Example 2b of the present invention. Is set to be B type in which the adjacent needle electrodes 10 are spaced apart from each other, and the radius r of the sphere Q inscribed in the most distal portion of the needle electrode 10 is set to 0. 0. The configuration of the present invention is the same as that of Example 1b except for the point set to 03 mm. In Example 2c, as a result of observing the close contact state with respect to the moving cooling body 5, data as shown in Table 2 below was obtained. From this data, in Examples 2a to 2c of the present invention, it is observed that streamer corona discharge is generated from each needle-like electrode 10 to the molten sheet-like body 4a at a predetermined interval, and the moving cooling body 5 is melted. It was confirmed that the sheet-like body 4a was in close contact in an appropriate state.

  On the other hand, the installation interval W of each needle electrode 10 is set to 6 mm, and a voltage of 3.5 kV is applied between the needle electrode 10 and the moving cooling body 5 to cause a current of 2.2 mA to flow. A comparative example 3a configured in the same manner as in Example 2a of the present invention except for the above-described points, a B-shaped needle electrode 10 is used, the applied voltage is set to 3.3 V, and a current value is set. In Comparative Example 3b configured in the same manner as Comparative Example 3a except that the value is set to 3.0 mm, when the moving speed of the moving cooling body 5 is set to 70 m / min, the moving cooling body 5 has a molten sheet. As a result, the thin body 4a could not be properly adhered, and in each case, thin pin-like defects were partially recognized on the surface of the sheet.

  Further, the radius of the sphere inscribed in the most distal portion of each needle-like electrode 10 is set to 0.1 mm, and a voltage of 4.9 kV is applied between the needle-like electrode 10 and the moving cooling body 5 to 3 A comparative example 4a configured in the same manner as in Example 2a except that a current of 0.0 mA was allowed to flow, and a B-shaped needle electrode 10 were used, and the needle electrode 10 and the molten sheet body 4a In Comparative Example 4b configured in the same manner as Comparative Example 4a except that the gap S was set to 1.5 mm and the applied voltage was set to 4.7 V, and the current value was set to 3.3 mm, When the moving speed of the moving cooling body 5 is set to 70 m / min, the molten sheet-like body 4a cannot be properly brought into close contact with the moving cooling body 5, and in all cases, pin-like defects are recognized on the entire sheet. Or streak-like defects were observed.

  Further, the apex angle θ of the tapered portion 10a provided at the tip of each needle electrode 10 is set to 120 °, and the radius of the sphere inscribed in the most distal portion of each needle electrode 10 is set to 0.03 mm. And a voltage of 4.9 kV is applied between the needle-like electrode 10 and the moving cooling body 5 to cause a current of 3.0 mA to flow, and is the same as Example 2c of the present invention. The same as Comparative Example 5a except that Comparative Example 5a configured as described above and B-shaped needle electrode 10 were used, the applied voltage was set to 4.7 V, and the current value was set to 3.3 mm. In the comparative example 5b configured as described above, when the moving speed of the moving cooling body 5 is set to 70 m / min, the molten sheet-like body 4a cannot be properly adhered to the moving cooling body 5, and both are pinned to the entire sheet. If a flaw is observed, or a streak is It was.

According to the method for producing a polyester-based resin sheet according to the present invention, a molten sheet-like body made of a thermoplastic resin having a high melting specific resistance, which has been difficult in the past, is appropriately electrostatically adhered to the moving cooling body, and the moving cooling is performed. Even when the moving speed of the body is increased, the molten sheet-like body can be appropriately cooled to increase the productivity of the sheet, which greatly contributes to the industry.

It is explanatory drawing which shows the whole structure of the manufacturing apparatus used for implementation of the manufacturing method of the polyester-type resin sheet of this invention. It is a side view which shows the installation state of a needle electrode. It is a front view which shows the installation state of a needle electrode. It is a front view which shows the other example of the installation state of a needle-shaped electrode. It is explanatory drawing which shows the structure of the front-end | tip part of a needle-like electrode. It is explanatory drawing which shows another example of the front-end | tip part of a needle-like electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Extruder 4a Molten sheet-like body 5 Moving cooling body 6 Corona discharge part 7,8 Extending part 10 Needle electrode 10a Tapered part Q Sphere r Radius θ Apex angle

Claims (2)

An extrusion process in which a polyester resin having a melting specific resistance value of 0.3 × 10 ⁸ (Ω · cm) or more is melted from an extruder into a sheet shape, and the molten sheet material extruded from the extruder is moved and cooled. In a method for producing a polyester-based resin sheet comprising a cooling step for closely contacting a body and cooling, and a stretching step for stretching a sheet-like body after cooling, a plurality of needle-like electrodes are orthogonal to the conveying direction of the molten sheet-like body A tapered portion in which a sphere having a radius of 0.01 mm to 0.05 mm is inscribed in the distal end portion circumferential surface is formed at the tip of the needle electrode, and the needle The gap between the electrode-like electrode and the molten sheet-like body is set within a range of 0.5 mm to 5 mm, and the installation interval of each needle-like electrode is less than 5 times the gap between the needle-like electrode and the molten sheet-like body. Corona discharge set A method for producing a polyester-based resin sheet, comprising: performing a streamer corona discharge on a molten sheet-like body in the cooling step from the machine to bring the molten sheet-like body into close contact with the moving cooling body and cooling. The method for producing a polyester-based resin sheet according to claim 1, wherein the apex angle of the tapered portion provided at the tip of the needle electrode is set to be less than 90 ° .

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