JP2019171705A - Polyamide film manufacturing apparatus and manufacturing method - Google Patents

Abstract

To be able to stably produce a polyamide film of excellent quality for a long time by suppressing a growth of oil balls that induce yellow foreign matter and die stripe defects on cast sheets, in an air knife method.SOLUTION: In a sheet cooling and forming apparatus that a resin sheet 5 is brought into close contact with a surface of a cooling roll 3 by bringing a polyamide resin 2 melt-extruded into a sheet form from a die 1 into contact with a surface of the cooling roll 3 and blowing an air flow from a slit nozzle 16 of an air knife 4, an outer dimension of the air knife 4 in a plane perpendicular to a width direction of the air knife 4 is expressed as that AH is a maximum dimension in a direction of blowing the air flow, and AW is the maximum dimension in an orthogonal direction. Then, AH is 1/2 or less of a length of an air gap, AW is 1/2 or less of AH, and a clearance of the slit nozzle is 0.2 mm or less.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a polyamide film manufacturing apparatus and manufacturing method, and more particularly, a polyamide film manufacturing apparatus and manufacturing focusing on a film forming process that is a cooling molding step of a cast sheet immediately after a molten resin extrusion process from a T-die. Regarding the method.

  In the method of forming a polyamide film by the T-die method, a polyamide resin is melt-extruded into a sheet form from a slit nozzle of the T-die, and this melt-extruded sheet is referred to as a cooling roll (hereinafter abbreviated as “CR”). And is cooled and solidified to form an unstretched cast sheet.

  As a method of pressing the melt-extruded sheet to the CR in the process of forming the polyamide film, a method in which a slit-like air flow is uniformly blown linearly in the width direction of the sheet from an air knife (hereinafter abbreviated as “air knife method”). However, it has been adopted conventionally. For example, Patent Document 1, Patent Document 2, Patent Document 3 and the like have descriptions thereof.

Japanese Patent No. 3369381 Japanese Patent No. 5822560 JP 2012-006271 A

  However, the air knife method has a problem that a defect called flat die, which impairs the flatness of the sheet, easily occurs on the lip surface of the T die.

  Specifically, low molecular weight substances such as monomers and oligomers generated from the molten polyamide resin adhere to the lip surface of the T die. Since these low molecular weight substances have a low melting point, they melt on the lip surface of the T-die heated to a high temperature to form oil droplets, and grow with the passage of operation time to become oil balls. This low molecular weight oil ball wets and spreads on the lip surface of the T-die while thermally degrading to brown. The oil balls sag and come into contact with the melt-extruded sheet extruded from the slit nozzle of the T die at the edge portion between the nozzle tip of the T die and the lip surface. When contact occurs, the oil balls are taken up by the melt-extruded sheet, and fine streaky yellow defects are generated on the surface of the melt-extruded sheet. In addition, at the edge portion where the yellow defect occurs, the molten resin causes expansion wetting also on the lip surface side, so that a thin streak-shaped die streak is subsequently generated on the cast sheet.

  Normally, the T-die is installed in the vicinity of the top of the CR so as to be inclined in the CR rotation direction. Therefore, these yellow foreign matters and die streak defects often occur on the surface of the sheet on the side where the air flow is blown by the air knife.

  The phenomenon in which the growth of oil balls that cause streak-like die streak defects in the T-die is accelerated is a problem inherent to the air knife method.

  At the time of melt extrusion of the polyamide resin, a large amount of monomer is generated by the depolymerization reaction. This monomer is an air gap (hereinafter sometimes abbreviated as “AG”) from the tip of the nozzle of the T-die to the contact line of the melt-extruded sheet on the CR. appear.

  On the other hand, the air flow blown from the air knife toward the contact line of the melt-extruded sheet on the CR is divided into the downstream side and the upstream side with respect to the flow direction of the sheet after hitting the melt-extruded sheet.

  The air stream on the upstream side, that is, the AG side that has been divided is an air flow that is opposite to the flow direction of the melt-extruded sheet along the AG, and blows toward the lip surface of the T-die while entraining the monomer gas. become. As a result, the growth of oil balls in the T-die is significantly accelerated.

  As a method of suppressing this phenomenon, for example,

  (1) A shielding plate is provided in the width direction of the sheet in the vicinity of the AG to shield the reverse airflow.

  (2) The air knife is retracted to a position where the AG becomes long and away from the T die.

(3) The air knife itself is reduced by reducing the slit clearance of the air knife.
Etc. However, both methods have the following problems. That is,

  In (1), low molecular weight substances such as monomers and oligomers adhere to the shielding plate and solidify, and white precipitates are deposited in a short time. If this scatters, it will become a foreign substance adhering on a sheet | seat.

  In (2), when AG is lengthened, the draft deformation stress at AG is lowered, so that the contact line of the melt-extruded sheet that is straight in the width direction on the CR is disturbed back and forth with respect to the running direction of the sheet. The wavy cooling unevenness occurs in the cast sheet.

  With regard to (3), a normal air knife is composed of a main body and an ejection nozzle, and the main body has a cylindrical header chamber having a C-shaped cross section over its entire width, and a fixed nozzle and a movable nozzle constituting a slit nozzle. Are fastened with bolts to both sides of the opening. In general, a high-pressure blower blows air into the header chamber and ejects an air flow in the width direction from the clearance of both nozzles. However, in this structure, deformation that causes the C-shaped cylinder to swell due to internal pressure occurs, and this deformation causes distortion at the tip of the slit nozzle, so-called opening phenomenon, so this type of air knife can narrow the clearance narrowly with high accuracy. Can not.

  No effective measures have been taken so far to suppress such problems specific to the air knife method, that is, the growth of oil balls that induce yellow foreign matter and die line defects on cast sheets.

  In production lines that require film products with strict quality requirements in recent years, in order to avoid these disadvantages, the production line must be periodically stopped to remove the oil balls adhering to the lip surface of the T-die. There was a hindrance to continuous productivity.

  As described above, the conventional technique has a problem in that it is not possible to ensure productivity that satisfies the cost performance industrially for high-quality polyamide films.

  Therefore, in the present invention, it is possible to stably produce an excellent quality polyamide film for a long period of time by suppressing the problem inherent to the air knife method, that is, the growth of oil balls that induce yellow foreign matter and die streak defects in cast sheets. The purpose is to do.

  The present invention relates to a sheet cooling molding apparatus in which a polyamide resin melt-extruded in a sheet form from a die is brought into contact with the surface of a cooling roll, and a resin sheet is closely adhered to the surface of the cooling roll by blowing an air flow from a slit nozzle of an air knife. ,

  Regarding the outer dimensions of the air knife in a plane perpendicular to the width direction of the air knife, where AH is the maximum dimension in the direction in which the air flow is blown and AW is the maximum dimension in the orthogonal direction, AH is 1 of the length of the air gap. 2 or less, AW is ½ or less of AH, and the clearance of the slit nozzle is 0.2 mm or less.

  According to the present invention, in the above manufacturing apparatus, a header pipe that supplies high-pressure air to an air knife that blows an air flow from a slit nozzle is provided at a position separated from the air knife on the downstream side in the sheet flow direction. The pipe and the air knife can be connected by a plurality of thin tubes in the width direction of the air knife.

  According to the present invention, in the above manufacturing apparatus, the angle formed by the wall portion at the tip of the air knife with respect to the direction in which the air flow is blown from the slit nozzle is upstream of the angle formed by the downstream wall portion in the sheet flow direction. The angle formed by the side wall portion is preferably an acute angle.

  According to the production method of the present invention, a polyamide film can be produced using the production apparatus described above.

  According to the production method of the present invention, it is possible to stretch a cast sheet which is cooled and molded by the above-described polyamide film production apparatus. In that case, biaxial stretching can be performed by a tenter driven by a linear motor system.

  According to the polyamide film manufacturing apparatus of the present invention, by reducing the size of the air knife and reducing the size of the air knife as compactly as possible, (1) diffusion without stagnation of the diverted air flow going back to the AG side it can. (2) Since the clearance of the nozzle of the air knife can be narrowed with high precision, the air volume itself of the air blown from the air knife can be reduced, and the diverted air flow backward to the AG side can also be reduced. These synergistic effects can suppress the growth of oil balls.

  Therefore, according to the present invention, it is unavoidable to stop the production line so far and to extend the rotation interval for cleaning the lip surface of the T die, and it is possible to stably produce a high quality polyamide film for a long time.

It is a front view explaining the manufacturing apparatus of the polyamide film of embodiment of this invention. It is a figure which shows the detail of the principal part in FIG. It is a top view of the principal part in FIG.

  1 to 3 show a film forming apparatus using an air knife method.

  Here, the sheet-like polyamide resin melt-extruded into a sheet form from the T-die 1 comes into contact with the surface of CR3 and is taken up by CR3. The air knife 4 applies air pressure to the sheet 5 to be brought into contact with the surface of the CR 3, and the sheet 5 is brought into close contact with the surface of the CR 3 to be cooled and solidified. As shown in detail in FIG. 3, the air knife 4 is connected to the header pipe 7 by a plurality of thin tubes 8 arranged in the width direction perpendicular to the paper surface of FIG. 1, that is, in the length direction of the air knife 4. High pressure air is supplied from the inside to the inside.

  The air knife 4 has a structure in which a shim is sandwiched between two plate-shaped air knife members having a two-part structure and fastened with bolts, and a slit-like nozzle is formed at one end of the air knife member, The thing of the system etc. which eject the high pressure air to the exterior through the slit-shaped nozzle from the supplied internal chamber can be mentioned. However, it is not particularly limited to these.

  In FIG. 1, 15 denotes the length of the air gap (AG) 13. As shown in FIG. 2, the polyamide film manufacturing apparatus of the present invention has a maximum shape dimension in the direction of blowing out an air flow of AH as the outer dimension of the air knife 4 in a plane perpendicular to the width direction of the air knife 4. Assuming that the maximum dimension in the direction orthogonal to the direction of blowing out the air flow is AW, AH is 1/2 or less of the length 15 of the air gap 13, AW is 1/2 or less of AH, and the air knife 4 It is most important to use the air knife 4 in which the clearance of the slit nozzle 16, that is, the opening width is 0.2 mm or less.

  In the film formation of a polyamide resin sheet, the length 15 of AG13 is usually 90 mm to 150 mm. By reducing the size of the air knife 4 with respect to the length 15 of the AG 13 so that AH is 1/2 or less of the length 15 of the AG 13 and AW is 1/2 or less of AH. , Does not inhibit the diffusion of the monomer gas generated in AG13, and does not disturb the diffusion of the diverted air flow on the AG13 side. As a result, generation and growth of oil droplets and oil balls in one T die can be suppressed.

  In the normal air knife composed of the main body and the jet nozzle described above, structurally, when the air pressure is applied to the inside, the main body is deformed to swell, thereby causing an opening phenomenon of the slit nozzle 16. The width, that is, the clearance cannot be kept narrow with high precision. Therefore, in the conventional large air knife, the nozzle clearance is set to 0.5 mm to 1.0 mm. This is the limit.

  However, in the present invention, by reducing the size of the air knife 4 as shown in FIG. 1, the distance from the inner chamber to the tip of the slit nozzle 16 can be designed to be short, so that deformation due to the mouth opening phenomenon is practically used. It can be stopped at a slight level of no problem.

  In order to adjust the clearance, it is relatively easy to finely adjust the clearance by alternately providing a push adjustment screw and a pull adjustment screw at predetermined intervals over the entire width in the vicinity of the straight land of the nozzle. In addition, it is more preferable because it can be adjusted with high accuracy and can fix and correct the opening distortion.

  The clearance of the slit nozzle 16 of the small air knife 4 used in the present invention is 0.2 mm or less as described above. More preferably, it is 0.1 mm or less.

  The tip lip of the air knife 4 is arranged to face the CR 3, but the distance between the tip lip and the CR 3 and the air pressure ejected from the air knife 4 are arbitrarily set within the range where the effect of pressing the sheet 5 against the CR 3 can be obtained. Can be set. Specifically, the distance between the tip lip of the air knife 4 and the CR 3 is usually 1 to 10 mm, preferably 1 to 5 mm. The jet air pressure is not particularly limited.

  As described above, the polyamide film manufacturing apparatus of the present invention has a header pipe 7 that supplies high-pressure air to the air knife 4 that blows an air flow from the slit nozzle 16, and a downstream of the sheet 5 in the flow direction of the sheet 5. A function-separated air that connects the header pipe 7 and the air knife 4 with a plurality of thin tubes 8 in the length direction, that is, the width direction of the air knife 4 installed between them at an arbitrary position separated to the side. A knife device can be used.

  As a method of installing the header pipe 7 and the air knife 4, there are a method in which the header pipe 7 is fixed to a support column and only the air knife 4 is movable, a method in which the header pipe 7 and the air knife 4 are movable in parallel, and the like. However, when it is necessary to largely retract the air knife 4 from the CR 3, the latter is preferable. Specifically, as shown in detail in FIG. 3, support arms 19 that support the air knife 4 are provided on the header pipe 7 on the left and right sides in the width direction of the seat 5, and the air knife 4 is appropriately separated from the header pipe 7. Install in parallel. Further, both left and right end portions of the header pipe 7 are attached to a column provided with a variable mechanism such as an XYθ positioning stage via a variable mechanism mounting bracket 20. Providing a variable mechanism is more preferable because the position and angle of the air knife 4 can be finely adjusted during operation. In FIG. 2, reference numeral 12 denotes an air supply port of the air knife 4, and a connecting thin tube 8 that supplies high-pressure air from the header pipe 7 is connected to the air supply port 12. High pressure air is introduced into the header pipe 7 from the high pressure air inlet 21.

  The air knife known so far is an integral type in which a fixed nozzle and a movable nozzle are fastened with bolts to a cylindrical large header chamber. In the polyamide film manufacturing apparatus of the present invention, an air flow is blown. The outer dimension of the air knife 4 can be reduced by separately providing the air knife 4 having the function of attaching and the header pipe 7 having the function of uniformly supplying high-pressure air to the air knife 4.

  The diameter size of the narrow tubes 8 connected from the header pipe 7 to the air knife 4 and the number and arrangement in the width direction can be any range in which the air flow to be blown out can be equalized and the sheet 5 can be uniformly cooled on the CR 3. Can be selected.

  The thin tube 8 to be connected is not particularly limited as long as it is a tubular body made of a material that can withstand the environment around the T-die 1 such as a polyurethane tube, a nylon tube, a tetrafluoroethylene resin tube, a SUS tube, or a soft copper tube. Absent.

  Further, by disposing the header pipe 7 away from the air knife 4, the diffusion of the air flow diverted from the air knife 4 in the flow direction of the blowing sheet 5 is not disturbed by the connecting thin tubes 8 and the header pipe 7. Specifically, the separation distance is 100 mm or more, preferably 200 mm or more in the shortest distance.

  In the polyamide film manufacturing apparatus of the present invention, the air knife 4 is formed in a tapered nozzle shape as shown in FIG. Specifically, the air knife 4 includes an upstream wall portion 17 in the sheet flow direction and a downstream wall portion 18 for constituting a tapered nozzle shape. 10 is an angle formed by the upstream wall portion 17 with respect to the direction in which the air flow 9 is blown from the slit nozzle 16, and 11 is an angle formed by the downstream wall portion 18 similarly. In FIG. 2, the two angles 10, 11 are equal. On the other hand, as another example, it is preferable that the angle 10 of the upstream wall portion 17 is more acute than the angle 11 of the downstream wall portion 18 in the sheet flow direction.

  The reason will be described below. The inclination of the spray angle of the air flow blown from the tip of the air knife 4 is set to be the downstream side in the flow direction of the sheet 5 with the normal line 19 of the CR 3 at the position of the contact line 6 of the AG 13 on the CR 3 as a base line. In other words, by depressing the air knife 4 to the AG side, it is possible to reduce the diverted air flow that goes back to the AG 13 side. However, when the air knife 4 is tilted to the AG 13 side, the wedge angle formed by the AG 13 and the wall portion of the air knife 4 is reduced, and the shunt air flow on the AG 13 side generates a vortex near the tip of the air knife 4. When the eddy current is generated, the atmospheric pressure at that position becomes a negative pressure, so that a phenomenon occurs that the molten extruded sheet 2 floats immediately before the contact line 6 of CR3. This disturbs the draft deformation of AG13, and the cast sheet 5 has wavy thickness unevenness.

  Whether or not this vortex is generated depends on the angle of the air flow 9 ejected from the tip of the air knife 4 with respect to the AG 13 side. The smaller the angle of the air flow 9 with respect to the AG 13 side, the more vortex generation can be suppressed. In order to reduce the angle of the air flow 9 with respect to the AG 13 side, the air knife 4 may be tilted toward the AG 13 side. The air knife 4 can be tilted as the angle 10 formed by the upstream wall portion 17 with respect to the direction in which the air flow 9 is blown from the slit nozzle 16 is made acute. For example, when the angle formed by the downstream wall 18 is 45 °, the angle formed by the upstream wall 17 is less than 30 °, so that the air knife 4 is tilted 10-20 ° toward the AG 13. be able to.

  As CR3, what has a structure where a cooling medium always circulates inside can be used. Examples of the surface material of CR3 include hard chrome plating and ceramic spray coating, but are not particularly limited thereto. Regarding the surface of CR3, it is preferable that the surface of the CR3 is roughened because an air layer interposed between the surface of CR3 and the sheet 5 is stabilized. Further, when CR3 is applied with ceramic spray coating, it is possible to reduce adhesion of the monomer contained in the melt-extruded sheet 2 that occurs in the process of cooling the sheet 5.

The temperature of the sheet 5 when it is cooled and solidified on the CR3 surface and then peeled off from the CR3 can be freely selected by setting the surface temperature of the CR3. The preferable film temperature at the time of peeling is in the range of 15 ° C. to Tg. The setting of the surface temperature of CR3 for this purpose can be performed by adjusting the temperature of the refrigerant circulating inside CR3 or by changing the surface roughness of CR3. When the peeling temperature is less than 15 ° C., water droplets are condensed on the surface of CR3, and uneven adhesion due to the water film causes trouble on the film formation. When the upper limit of the peeling temperature is higher than the glass transition point Tg of the polyamide resin, peeling from the CR3 becomes difficult, and the sheet 5 is stretched in the vertical direction due to peeling stress, so that the thickness and flatness of the sheet 5 are greatly impaired. It is.
The cast sheet 5 cooled by the air knife method according to the present invention can be further stretched to produce a stretched polyamide film.

  As the stretching method, various methods such as a longitudinal or lateral uniaxial stretching method, a sequential biaxial stretching method, and a simultaneous biaxial stretching method can be applied. Of these, the sequential biaxial stretching method and the simultaneous biaxial stretching method are preferable. Simultaneous biaxial stretching methods include pantograph type, screw type, linear motor type, etc., depending on the driving method of the clip. In particular, the linear motor type tenter, in which the clip is individually driven by the linear motor, has excellent high-speed running performance. Therefore, it is preferable.

  Nylon 6 and nylon 66 are typical examples of the polyamide resin constituting the film produced according to the present invention. In addition, homopolymers such as nylon 11 and nylon 12 can also be used. Further, a mixture or copolymer of these polyamide resins can also be used. The polyamide resin may contain a known additive such as a stabilizer, an antioxidant, a filler, a lubricant, an antistatic agent, an antiblocking agent, a colorant and the like.

  First, sample evaluation methods in the following examples and comparative examples will be described.

(1) Thickness unevenness Using an in-line infrared thickness gauge, the thickness of the stretched film was measured while scanning in the width direction. As the thickness gauge, an infrared thickness gauge (FG710S) manufactured by NDC was used. The spot diameter at the measurement point was 5 mm in diameter and the measured values were taken at a pitch of 15 mm in the width direction, and the thickness unevenness was monitored at 2σ.

(2) Polarizing plate observation The first polarizing plate is placed on the light source and fixed, the test film is placed thereon, the second polarizing plate is further stacked, and the second polarizing plate is observed while being rotated. The evaluation was made according to the following criteria.
○: No unevenness is observed at all and good Δ: Unevenness is not observed ×: Wavy unevenness is observed and defective

[Example]
The polyamide resin was melt-extruded into a sheet at an extrusion temperature of 260 ° C. using an extruder having a diameter of 115 mm and a T-die having a width of 630 mm. The melt-extruded sheet was cooled on a CR spray having a diameter of 1200 mm coated on the surface by an air knife method to form a cast sheet having a thickness of 150 μm. Next, the obtained cast sheet is passed through a water absorption treatment device having a water temperature of 50 ° C., and then continuously stretched 3.0 times in the longitudinal direction and 3.3 times in the transverse direction by a simultaneous biaxial stretching machine. A biaxially stretched polyamide film having a thickness of 15 μm was obtained.

  At that time, using a small air knife (AH: 45 mm, AW: 20 mm, slit nozzle clearance: 0.1 mm) with a width of 630 mm, the AG length is 100 mm, and the distance between the tip of the air knife and the CR is 3 mm. The melt-extruded sheet was pressed against the surface of the CR by blowing an air flow from an air knife. The surface temperature of the CR was adjusted to 20 ° C.

  The results are shown in Table 1. Even when 24 hours passed at a production rate of 150 m / min, the thickness unevenness 2σ was 0.8 μm. Further, no dice lines were observed even when observing the polarizing plate, and the production was stable.

[Comparative example]
The air knife was replaced with a normal large type, that is, an integral large type (slit nozzle clearance: 0.5 mm) in which a fixed nozzle and a movable nozzle are fastened to a cylindrical large header chamber with bolts. Other than that was carried out similarly to said Example, and obtained the biaxially stretched polyamide film.

  The results are shown in Table 1. After 12 hours, the thickness unevenness 2σ increased to 1.2 μm, and streaky unevenness was confirmed by polarizing plate observation. For this reason, in order to ensure quality, the line was stopped and the lip of the T die had to be washed.

DESCRIPTION OF SYMBOLS 1 T die 2 Melt extrusion sheet 3 Cooling roll 4 Air knife 5 Sheet 7 Header pipe 8 Narrow tube 10 Angle 11 Angle 13 Air gap (AG)
15 Length 16 Slit nozzle 17 Wall 18 Wall 19 Support arm 20 Variable mechanism mounting bracket 21 High pressure air inlet AH Maximum dimension AW Maximum dimension

Claims (6)

In the sheet cooling molding apparatus in which the polyamide resin melt-extruded in a sheet form from the die is brought into contact with the surface of the cooling roll, and the resin sheet is brought into close contact with the surface of the cooling roll by blowing an air flow from a slit nozzle of an air knife.
Regarding the outer dimensions of the air knife in a plane perpendicular to the width direction of the air knife, where AH is the maximum dimension in the direction in which the air flow is blown and AW is the maximum dimension in the orthogonal direction, AH is 1 of the length of the air gap. / 2, or less, AW is ½ or less of AH, and the clearance of the slit nozzle is 0.2 mm or less.   A header pipe that supplies high-pressure air to an air knife that blows an air flow from a slit nozzle is provided at a position separated from the air knife to the downstream side in the sheet flow direction, and between the header pipe and the air knife, The apparatus for producing a polyamide film according to claim 1, wherein the polyamide film is connected by a plurality of thin tubes in the width direction.   With respect to the angle formed by the wall portion at the tip of the air knife with respect to the direction in which the air flow is blown from the slit nozzle, the angle formed by the upstream wall portion is more acute than the angle formed by the downstream wall portion in the sheet flow direction. The apparatus for producing a polyamide film according to claim 1 or 2.   A polyamide film production method using the polyamide film production apparatus according to any one of claims 1 to 3.   The method for producing a polyamide film according to claim 4, wherein the cast sheet formed by cooling with a polyamide film production apparatus is stretched.   6. The method for producing a polyamide film according to claim 5, wherein biaxial stretching is performed by a tenter driven by a linear motor system.

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