JP7141683B2 - Polyamide film manufacturing apparatus and manufacturing method - Google Patents

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 method focusing on a film forming process, which is a cooling molding stage of a cast sheet immediately after the process of extruding a molten resin from a T-die. Regarding the method.

In the method of producing a polyamide film by the T-die method, the polyamide resin is melt-extruded into a sheet from the slit nozzle of the T-die, and the melt-extruded sheet is passed through a cooling roll called a casting roll (hereinafter abbreviated as "CR" ) and cooled and solidified to form an unstretched cast sheet.

As a method of pressing the melt extruded sheet against the CR in the process of producing a polyamide film, a method of linearly and uniformly blowing a slit-shaped air flow in the width direction of the sheet from an air knife (hereinafter abbreviated as "air knife method"). has been conventionally used. For example, Patent Document 1, Patent Document 2, Patent Document 3, etc., have descriptions thereof.

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

However, in the air knife method, there is a problem that defects called die streaks, which impair the flatness of the sheet, tend to occur on the lip surface of the T die.

Specifically, low molecular 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 low melting points, they melt to form oil droplets on the lip surface of the T-die, which is heated to a high temperature. This low-molecular-weight oil ball wets and spreads on the lip surface of the T-die while thermally deteriorating to a brown color. The oil droplets drip and contact the melt extruded sheet extruded from the slit nozzle of the T-die at the edge between the tip of the nozzle of the T-die and the lip surface. When contact occurs, the oil droplets are drawn into the melt-extruded sheet, causing thin streak-like yellow defects on the surface of the melt-extruded sheet. In addition, at the edge portion where the yellow defect is generated, the molten resin spreads out on the lip surface side as well, so that fine streak-like die streaks are subsequently generated on the cast sheet.

Since the T-die is usually installed near the top of the CR at an angle in the direction of rotation of the CR, these yellow foreign matter and die streak defects often occur on the side of the sheet to which the air knife blows the air flow.

The phenomenon of accelerated growth of oil droplets that causes streak-like die streak defects in the T die is a problem unique to the air knife method.

During melt extrusion of polyamide resin, a large amount of monomer is produced by depolymerization reaction. This monomer is extruded from the molten polyamide resin at a high temperature in an air gap (hereinafter sometimes abbreviated as "AG") from the nozzle tip of the T die to the contact line of the molten extruded sheet on the CR as a monomer gas. Occur.

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 split into the downstream side and the upstream side with respect to the flow direction of the sheet after hitting the melt extruded sheet.

This split upstream side, that is, the AG side air flow becomes an air flow that runs counter 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 droplets is significantly accelerated in the T-die.

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 diverted air flow that goes backward.

(2) Retract the air knife to a position where AG becomes longer, and keep it away from the T die.

(3) The slit clearance of the air knife is narrowed to reduce the amount of jetted air.
etc. However, both methods have the following problems. i.e.

In (1), low-molecular-weight substances such as monomers and oligomers adhere to the shielding plate and solidify, depositing a white deposit in a short period of time. When this scatters, it becomes an adhering foreign matter on the sheet.

In (2), the longer the AG, the lower the draft deformation stress in the AG, so the contact line of the melt extruded sheet, which was straight in the width direction on the CR, is disturbed back and forth in the running direction of the sheet. , Wavy uneven cooling occurs in the cast sheet.

Regarding (3), a normal air knife consists of a main body and a jet nozzle. are bolted to both sides of the opening. Generally, a high-pressure blower blows air into the header chamber and blows out the air flow in the width direction from the clearance of both nozzles. However, with this structure, the C-shaped cylinder swells due to internal pressure, and this deformation causes distortion at the tip of the slit nozzle, the so-called mouth opening phenomenon. Can not.

No effective countermeasures have been taken so far to suppress the problems inherent in the air knife method, that is, the growth of oil droplets that cause yellow foreign matter on cast sheets and die streak defects.

In order to avoid these shortcomings, production lines that require film products with strict quality requirements in recent years have to stop the production line periodically to remove oil droplets adhering to the lip surface of the T-die. There was an obstacle to continuous productivity.

As described above, the conventional techniques have the problem that it is not possible to ensure industrial productivity that satisfies cost performance for high-quality polyamide films.

Therefore, in the present invention, it is possible to stably produce a polyamide film of excellent quality for a long time by suppressing the problem inherent to the air knife method, that is, the growth of oil droplets that induce yellow foreign matter on the cast sheet and die streak defects. intended to

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

With regard to the outer dimensions of the air knife in the plane perpendicular to the width direction of the air knife, AH is the maximum dimension in the direction in which the air flow is blown out, and AW is the maximum dimension in the direction perpendicular to that direction. /2 or less, AW is 1/2 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-described manufacturing apparatus, a header pipe for supplying high-pressure air to an air knife for blowing an air flow from the slit nozzle is provided at a position spaced downstream from the air knife in the sheet flow direction, and the header pipe The pipe and the air knife may be connected in the width direction of the air knife with a plurality of fine tubes.

According to the present invention, in the above-described 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 greater than the angle formed by the wall portion on the downstream side in the flow direction of the sheet. Preferably, the angle between the side walls is more acute.

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

According to the manufacturing method of the present invention, the cast sheet that has been cold-molded by the above-described polyamide film manufacturing apparatus can be stretched. In that case, it can be biaxially stretched by a tenter driven by a linear motor system.

According to the polyamide film manufacturing apparatus of the present invention, by making the air knife as compact as possible by reducing the external dimensions of the air knife, (1) the diverted air flow going backward to the AG side is diffused without staying. can. (2) Since the clearance of the nozzle of the air knife can be narrowed with high precision, the air volume itself of the jetted air from the air knife can be reduced, and the diverted air flow going backward to the AG side can also be reduced. These synergistic effects can suppress the growth of oil droplets.

Therefore, according to the present invention, it is possible to extend the rest interval, which has hitherto been unavoidable to stop the production line and wash the lip surface of the T-die, and to stably produce a high-quality polyamide film for a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS It is a front view explaining the manufacturing apparatus of the polyamide film of embodiment of this invention. FIG. 2 is a diagram showing details of a main part in FIG. 1; FIG. 2 is a plan view of a main part in FIG. 1;

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

Here, the sheet-like polyamide resin melt-extruded from the T-die 1 comes into contact with the surface of the CR3 and is taken up by the CR3. The air knife 4 applies air pressure to the sheet 5 which is about to contact the surface of the CR3, and the sheet 5 is brought into close contact with the surface of the CR3 and 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 narrow tubes 8 arranged in the width direction perpendicular to the plane of FIG. 1, ie, the length direction of the air knife 4. high-pressure air is supplied to the inside thereof from.

The air knife 4 has a structure in which a shim is sandwiched between plate-shaped air knife members of a two-part structure and bolted together, and a slit-shaped nozzle is formed at one end of the air knife member. For example, a system in which the high-pressure air is ejected to the outside through a slit-like nozzle from an internal chamber to which it is supplied can be used. However, it is not particularly limited to these.

In FIG. 1, 15 indicates the length of the air gap (AG) 13 . As shown in FIG. 2, in the polyamide film manufacturing apparatus of the present invention, regarding the external dimensions of the air knife 4 in the plane perpendicular to the width direction of the air knife 4, the maximum dimensions in the air blowing direction are AH and AH, respectively. Letting AW be the maximum dimension in the direction perpendicular to the direction in which the air flow is blown out, 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 length of the air knife 4 is It is most important to use the air knife 4 with the clearance of the slit nozzle 16, that is, the opening width of 0.2 mm or less.

In the production of polyamide resin sheets, the length 15 of the AG 13 is usually 90 mm to 150 mm. By miniaturizing 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. , the diffusion of the monomer gas generated in the AG 13 is not hindered, and the diffusion of the diverted air flow on the AG 13 side is not hindered. As a result, the generation and growth of oil droplets and oil droplets on the T-die 1 can be suppressed.

In an ordinary air knife composed of the above-described main body and jet nozzle, structurally, when air pressure is applied to the interior, deformation occurs in which the main body swells, which causes the slit nozzle 16 to open. Width or clearance cannot be maintained narrow with high accuracy. Therefore, in conventional large air knives, the nozzle clearance is set to 0.5 mm to 1.0 mm. This is the limit.

However, in the present invention, by miniaturizing the air knife 4 as shown in FIG. 1, the distance from the internal chamber to the tip of the slit nozzle 16 can be shortened, so that deformation due to the opening phenomenon can be practically reduced. It can be stopped at a slight distortion of a problem-free level.

In order to adjust this clearance, it is relatively easy to finely adjust the clearance by alternately providing push adjustment screws and pull adjustment screws at predetermined intervals over the entire width near the straight land of the nozzle. This is more preferable because highly accurate adjustment is possible and the opening distortion can be fixed and corrected here.

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 CR3, but the distance between the tip lip and the CR3 and the air pressure jetted from the air knife 4 can be arbitrarily set within the range in which the effect of pressing the sheet 5 against the CR3 can be obtained. can be set. Specifically, the distance between the tip lip of the air knife 4 and the CR3 is usually 1 to 10 mm, preferably 1 to 5 mm. The ejection air pressure is not particularly limited.

In the polyamide film manufacturing apparatus of the present invention, as described above, the header pipe 7 for supplying high-pressure air to the air knife 4 that blows air from the slit nozzle 16 is positioned downstream from the air knife 4 in the flow direction of the sheet 5 . The header pipe 7 and the air knife 4 are connected to each other by a plurality of fine tubes 8 in the length direction, that is, the width direction of the air knife 4, which are provided at arbitrary positions apart from each other and installed between them. A knife device can be used.

As a method of installing the header pipe 7 and the air knife 4, a method of fixing the header pipe 7 to a support and moving only the air knife 4, a method of moving the header pipe 7 and the air knife 4 in parallel, and the like can be considered. However, the latter is preferable when the air knife 4 needs to be largely retracted from the CR3. Specifically, as shown in detail in FIG. Install parallel. Furthermore, the left and right ends of the header pipe 7 are attached to a column provided with a variable mechanism such as an XY.theta. By providing a variable mechanism, the position and angle of the air knife 4 can be finely adjusted during operation, which is more preferable. 2, reference numeral 12 denotes an air supply port of the air knife 4, to which a connecting thin pipe 8 for supplying high pressure air from the header pipe 7 is connected. High-pressure air is introduced into the header pipe 7 from a high-pressure air inlet 21 .

Conventionally known air knives are an integrated type in which a fixed nozzle and a movable nozzle are bolted to a large cylindrical header chamber. By separately providing the air knife 4 with the function of attaching and the header pipe 7 with the function of uniformly supplying high-pressure air to the air knife 4, the external dimensions of the air knife 4 can be reduced.

The diameter size, width direction number and arrangement of the thin tubes 8 connecting the header pipe 7 to the air knife 4 are set within an arbitrary range so as to equalize the pressure of the blown air flow and to obtain uniform cooling of the sheet 5 on the CR 3. can be selected by

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, nylon tube, tetrafluoroethylene resin tube, SUS tube, or soft copper tube. do not have.

Further, by setting the header pipe 7 away from the air knife 4, the diffusion of the air flow branched from the air knife 4 in the flow direction of the blowing sheet 5 is not hindered by the connecting fine tubes 8 and the header pipe 7.例文帳に追加Specifically, the minimum separation distance is 100 mm or more, preferably 200 mm or more.

In the polyamide film manufacturing apparatus of the present invention, as shown in FIG. 2, the air knife 4 is formed into a tapered nozzle shape. Specifically, the air knife 4 comprises an upstream wall portion 17 and a downstream wall portion 18 in the sheet flow direction for forming a tapered nozzle shape. Reference numeral 10 denotes an angle formed by the wall portion 17 on the upstream side with respect to the direction in which the air flow 9 is blown from the slit nozzle 16, and 11 denotes an angle formed by the wall portion 18 on the downstream side. In FIG. 2 both angles 10, 11 are shown to be equal. On the other hand, as another example, it is preferable that the angle 10 of the wall 17 on the upstream side in the flow direction of the sheet is sharper than the angle 11 of the wall 18 on the downstream side.

The reason is explained below. With the normal line 19 of the CR3 at the position of the contact line 6 of the AG 13 on the CR3 as the base line, the inclination of the blowing angle of the air flow blown from the tip of the air knife 4 is directed downstream in the flow direction of the sheet 5. In other words, by tilting the air knife 4 toward the AG side, it is possible to reduce the diverted air flow going backward to the AG 13 side. However, when the air knife 4 is tilted toward the AG 13 side, the wedge angle formed by the AG 13 and the wall portion of the air knife 4 becomes small, and the branched air flow on the AG 13 side generates a swirl near the tip of the air knife 4 . When a vortex is generated, the atmospheric pressure at that position becomes a negative pressure, and a phenomenon occurs in which the melt extruded sheet 2 floats just before the contact line 6 of the CR3. This disturbs the draft deformation of the AG 13 and causes the cast sheet 5 to have wavy unevenness in thickness.

Whether or not this vortex is generated depends on the angle of the airflow 9 jetted from the tip of the air knife 4 with respect to the AG 13 side. The smaller the angle of the airflow 9 with respect to the AG 13 side, the more the vortex 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 should be tilted toward the AG 13 side. The more acute the angle 10 formed by the wall portion 17 on the upstream side with respect to the direction in which the air flow 9 is blown from the slit nozzle 16, the more the air knife 4 can be tilted. For example, when the angle formed by the wall portion 18 on the downstream side is 45°, by setting the angle formed by the wall portion 17 on the upstream side to less than 30°, the air knife 4 is tilted toward the AG 13 by 10 to 20°. be able to.

As the CR3, one having a structure in which a cooling medium is constantly circulated inside can be used. Surface materials of CR3 include hard chromium plating, ceramic thermal spray coating, etc., but are not particularly limited to these. As for the surface of the CR3, it is preferable to roughen the surface because the air layer interposed between the surface of the CR3 and the sheet 5 is stabilized. In addition, CR3 coated with a ceramic spray coating can reduce adhesion of monomers contained in the melt-extruded sheet 2 during the process of cooling the sheet 5 .

The temperature of the sheet 5 when it is separated from the CR3 after being cooled and solidified on the surface of the CR3 can be freely selected by setting the surface temperature of the CR3. The preferred film temperature during peeling is in the range of 15°C to Tg. The surface temperature of the CR3 can be set for this purpose by adjusting the temperature of the coolant circulating inside the CR3 or by changing the surface roughness of the CR3. If the peeling temperature is less than 15° C., water droplets will condense on the surface of CR3, and uneven adhesion due to the water film will cause problems in film formation. When the upper limit of the peeling temperature is higher than the glass transition point Tg of the polyamide resin, peeling from CR3 becomes difficult, and the peel stress stretches the sheet 5 in the vertical direction, so the thickness and flatness of the sheet 5 are greatly impaired. be
The cast sheet 5 that has been cooled and molded 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 transverse uniaxial stretching method, a sequential biaxial stretching method, and a simultaneous biaxial stretching method can be applied. Among them, the sequential biaxial stretching method and the simultaneous biaxial stretching method are preferable. The simultaneous biaxial stretching method includes the pantograph type, screw type, linear motor type, etc., depending on the clip driving method. In particular, the linear motor type tenter, in which the clips are individually driven by a linear motor, is excellent in high-speed running performance. It is preferable because

Nylon 6 and nylon 66 are typical polyamide resins constituting the film produced by the present invention. In addition, homopolymers such as nylon 11 and nylon 12 can also be used. Furthermore, mixtures and copolymers of these polyamide resins can also be used. The above polyamide resin may contain known additives such as stabilizers, antioxidants, fillers, lubricants, antistatic agents, antiblocking agents and colorants.

First, a method for evaluating samples 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 a thickness gauge, an NDC infrared thickness gauge (FG710S) was used. The spot diameter of the measurement points was φ5 mm, 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) Observation of polarizing plate The first polarizing plate is placed and fixed on the light source, the test film is placed on top of it, and the second polarizing plate is overlaid, and observation is made while rotating this second polarizing plate. and evaluated according to the following criteria.
○: Good with no unevenness observed △: Limit where unevenness is not observed ×: Poor with wavy unevenness observed

[Example]
Using an extruder with a diameter of 115 mm and a T-die with a width of 630 mm, the polyamide resin was melt-extruded into a sheet at an extrusion temperature of 260°C. The melt-extruded sheet was brought into close contact with a CR having a diameter of 1200 mm, the surface of which was coated with ceramic by thermal spraying, by an air knife method, and cooled to form a cast sheet having a thickness of 150 μm. Next, the obtained cast sheet was passed through a water absorption treatment device with 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 with a simultaneous biaxial stretching machine. , to obtain a biaxially stretched polyamide film having a thickness of 15 μm.

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

Table 1 shows the results. Even after 24 hours at a production speed of 150 m/min, the thickness unevenness 2σ was 0.8 μm. Also, no die streaks were observed in the observation of the polarizing plate, and the production was stable.

[Comparative example]
The air knife was replaced with a normal large type, that is, an integrated large type (clearance of slit nozzle: 0.5 mm) in which a fixed nozzle and a movable nozzle are bolted to a large tubular header chamber. Otherwise, a biaxially stretched polyamide film was obtained in the same manner as in the above Examples.

Table 1 shows the results. After 12 hours, the thickness unevenness 2σ increased to 1.2 μm, and stripe-like unevenness was confirmed by observing the polarizing plate. Therefore, in order to ensure quality, the line had to be stopped and the lip of the T-die had to be washed.

1 T-die 2 Melt extruded sheet 3 Cool roll 4 Air knife 5 Sheet 7 Header pipe 8 Capillary 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 (5)

In a sheet cooling molding device, a polyamide resin melt-extruded into a sheet from a die is brought into contact with the chill roll surface, and an air flow is blown from a slit nozzle of an air knife to adhere the resin sheet to the chill roll surface.
A header pipe for supplying 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 downstream in the sheet flow direction,
the header pipe and the air knife are connected in the width direction of the air knife by a plurality of fine tubes,
An air knife is provided across the width of the die,
With regard to the outer dimensions of the air knife in the plane perpendicular to the width direction of the air knife, AH is the maximum dimension in the direction in which the air flow is blown out, and AW is the maximum dimension in the direction perpendicular to that direction. /2 or less, AW is 1/2 or less of AH, and the clearance of a slit nozzle is 0.1 mm or less. Regarding the angle formed by the wall portion of 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 wall portion on the upstream side in the flow direction of the sheet is more acute than the angle formed by the wall portion on the downstream side. The apparatus for producing a polyamide film according to claim 1, characterized in that: 3. A method for producing a polyamide film, comprising using the apparatus for producing a polyamide film according to claim 1 or 2. 4. The method for producing a polyamide film according to claim 3, wherein the cast sheet that has been cooled and molded in a polyamide film production apparatus is stretched. 5. The method for producing a polyamide film according to claim 4, wherein the film is biaxially stretched by a tenter driven by a linear motor system.

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