JPH1134144A - Manufacture of polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyester film containing polyethylene naphthalate from which fine foreign matter is highly removed as a main component with high productivity. SOLUTION: The method for manufacturing a polyester film comprises the steps of melting polyester of 2,6-ethylene naphthalate unit of 70 to 100 mol.% of total repeating unit, filtering it, and then melt extruding it in a sheet-like state. In this case, it is filtered by a heat resistant fiber filter having an interstice of a range of 1 to 20 μm and a void fraction of a range of 50 to 90%, and then by a filtering unit having at lest one filter having a pore side of converting from an input side of the melt polyester toward a discharge side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester film by melt-extruding polyester to produce a polyester film.

[0002]

2. Description of the Related Art Polyethylene terephthalate (PET)
Are widely used as molding materials for fibers, films, transparent containers, etc. Recently, polyethylene naphthalate (PEN) has higher strength and flexibility than polyethylene terephthalate. Has attracted attention. Research has been conducted on using PEN to improve the quality of electrical components, supports for photographic films, supports for magnetic recording media, transparent containers, and the like. Typical examples of photographic films include those in sheet form, such as X-ray film, plate making film (eg, negative or positive film for producing integrated circuits) and cut film, and those in roll form. It has been known. A typical roll film is 35mm
135-type film, which is a color film or a black-and-white negative film loaded into a general camera and used for photographing, which is housed in a patrone with a width, and wide-type brownie films (eg, 120-type and 220-type) Can be. Conventionally, a cellulose triacetate (TAC) film has been used as a support for a 135 type or brownie type film as a roll film. T
The AC film has no optical anisotropy and high transparency, and also has excellent curl-removing properties after development, and has good properties as a photographic support.

On the other hand, in response to a demand for miniaturization of a camera or a miniaturization of a patrone, thinning of a photographic support has been studied and has already been put to practical use. At that time, the use of the TAC was also studied, but there was a problem that if the TAC was thinned, the strength required for the photographic support was not satisfied. Therefore, high strength polyethylene terephthalate (PE)
T), polyethylene-2,6-naphthalate (PEN)
The study was advanced using polyesters such as. When a thin film is made of PET which has been conventionally used for a sheet-like film, the obtained film has a problem that curling due to curling is liable to occur. Since the PEN exhibited excellent properties, a thin film was realized using this PEN (EP0606070A1, JP-A-7-72584). This PEN film is used as a support for a new camera system, the Advanced Photo System (APS).

[0004] PEN films are much more preferable than PET films as supports for photographic films used in rolls because they have excellent heat resistance and are unlikely to have curl. However, the PEN has a problem that it has more foreign substances than TAC, which is a material conventionally used as a support of a roll-shaped photographic film.

[0005] PEN capable of reducing this foreign matter
Are described in JP-A-6-80772 and JP-A-7-268190. These publications state that antimony compounds, which are catalysts usually used for polycondensation of PEN, are liable to form foreign substances, and therefore it is preferable to use a catalyst mainly composed of a germanium compound. He pointed out that antimony compounds are the main cause of foreign substances. However, although the PEN film obtained by polymerization in such a manner has few foreign substances and improved transparency, the crystallinity of the film is reduced, so that the film is formed by, for example, biaxial stretching. , It is difficult for crystallization due to stretching to occur,
There is a problem that a film with a sufficiently uniform orientation cannot be obtained.

On the other hand, in order to prevent the polymerization reaction of PEN from being restricted, a method of reducing foreign substances by filtration performed during the polymerization step or the melt extrusion step has been studied. However, PET has a lower melting temperature and lower viscosity during melting than PEN (20
(About 00 poise), it is easy to filter foreign substances up to about 30 microns without deteriorating the polymer.
PEN has a high melting point and a high viscosity when melted,
In order to remove foreign matter to the same degree as ET, it is necessary to apply a high pressure at the time of filtration, so that there is a problem that a heavy load is applied to the apparatus and the polymer may be deteriorated.
By removing foreign matter up to about 30 microns as described above, it can be used as a support for a negative film when exposing to a photosensitive resin for producing an integrated circuit or the like. Cannot be used on the body. That is, in order to use a PEN film as a support for a photographic film, it is necessary to remove a very small amount of fine particles having a size of 20 μm or less, and a PEN film cannot be obtained by a filtration method similar to PET. Therefore, 2
In order to obtain a PEN film reduced to minute foreign substances of 0 μm or less, it is necessary to perform filtration for a long time and with low productivity while placing a great burden on the apparatus.

[0007]

As described above, PEN
Has a higher melting temperature than PET and a higher viscosity at the time of melting. Therefore, even if filtration is performed using a heat-resistant fiber filter having a mesh size of 1 to 50 μm, which is generally used for PET filtration, filtration is not possible. In addition, a high pressure is required, which imposes a heavy burden on the apparatus, and the filter is liable to be clogged. In addition, when filtration is performed at a low speed, the polymer tends to deteriorate. Therefore, the present inventor
A method has been studied which can be used to filter the polymer at an appropriate speed without deterioration of the polymer. That is, in order to obtain a PEN film reduced to minute foreign substances of 20 μm or less with a high productivity as in PET, a study on a filtration method at the time of melt extrusion has been repeated. Then, they found that this can be achieved by using a filter having a specific structure, and arrived at the present invention. An object of the present invention is to provide a method for producing a polyester film containing polyethylene naphthalate as a main component from which fine foreign substances have been highly removed, with high productivity.

[0008]

According to the present invention, there is provided a method for melting and extruding a polyester in which 70 to 100 mol% of all the repeating units are 2,6-ethylenenaphthalate units, and then extruding the sheet into a sheet. In the method for producing a polyester film, the filtration is performed with an aperture of 1 to 20 μm.
m, and has a porosity in the range of 50 to 90%, and is changed so that the pore diameter of the voids decreases from the inflow side to the discharge side of the molten polyester. A method for producing a polyester film, wherein the method is performed using a filtration device having at least one filter.

Preferred embodiments of the production method of the present invention are as follows. 1) The aperture is in the range of 1 to 15 μm. 2) The porosity is in the range of 60 to 90%. 3) The heat-resistant fiber is a metal fiber. 4) The filter is composed of at least a region having a large pore size on the inflow side of the molten polyester and a region having a small pore size inside the region. 5) In the filter according to 4) above, the region of a large pore diameter on the inflow side includes a range of 20 to 50 μm and 10 to 20 μm.
A region having a pore size distribution within the range of 0 μm, and a region having a small pore size inside the region is a region including a range of 3 to 10 μm and having a pore size distribution within a range of 1 to 50 μm. 6) The filter is a heat-resistant fiber filter having an opening in the range of 1 to 5 μm and a porosity in the range of 50 to 90%, and has a smaller pore size from the inflow side to the discharge side of the molten polyester. Filter having a mesh size in the range of 6 to 20 μm, and a porosity of 50 to 90 μm.
% Of the heat-resistant fiber and two filters. 7) The repeating unit other than the 2,6-ethylene naphthalate unit of the polyester is an ethylene terephthalate unit. That is, 0 to 30 mol% of all repeating units of the polyester are ethylene terephthalate units. 8) At least one wire mesh in the range of 10 to 500 mesh (in the case of two pieces, the wire mesh on the surface and the wire mesh thereover are laminated on the inlet side surface of the filter so that the mesh size increases in order. Be installed). 9) At least one wire mesh in the range of 10 to 200 mesh is provided on the outlet side surface of the filter.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The production method of the present invention uses polyethylene-2,6-naphthalate or ethylene-2,6-
Copolymer containing naphthalate unit as main component (eg, copolymer of ethylene naphthalate and ethylene terephthalate)
Alternatively, when a polyester film is produced by melt-extruding a mixture (eg, PEN and PET) containing polyethylene-2,6-naphthalate as a main component, the method is characterized by a filtration method before the melt extrusion. A polyester film is produced by the production method of the present invention, and the polyester having the ethylene-2,6-naphthalate unit as a main component is used for producing the polyester film. In the polybasic acid used for the synthesis of the polyester, at least 70 mol% of the total polybasic acid is 2,6-naphthalenedicarboxylic acid or a lower alkyl ester of 2,6-naphthalenedicarboxylic acid (that is, dialkyl) (purity). Dimethyl 2,6-naphthalenedicarboxylate is preferred). As the lower alkyl, methyl, ethyl, isopropyl, propyl, or butyl is preferable, and methyl is particularly preferable.

In general, terephthalic acid, isophthalic acid, phthalic acid, 2,7-
Aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid and diphenyldicarboxylic acid and lower alkyl esters thereof (lower alkyl is preferably methyl, ethyl, isopropyl, propyl or butyl, particularly preferably methyl) used. Particularly, isophthalic acid and its lower alkyl ester are preferred. Other polybasic acids include alicyclic dicarboxylic acids such as cyclopropanedicarboxylic acid, cyclobutanedicarboxylic acid, and hexahydroterephthalic acid, and lower alkyl esters thereof (preferable alkyl is the same as described above); and adipic acid, succinic acid, and oxalic acid. Aliphatic dicarboxylic acids such as acids, azelaic acid, sebacic acid and dimer acid and their lower alkyl esters (preferably alkyl is the same as above) may be used in an amount of 10 mol% or less.

In the polyhydric alcohol used for the synthesis of the polyester, at least 70 mol% of all the polyhydric alcohol is ethylene glycol (boiling point: 198 ° C.). It is preferably at least 90 mol%, particularly preferably 100 mol%. Other polyhydric alcohols include propylene glycol, trimethylene glycol, diethylene glycol,
Tetramethylene glycol, hexamethylene glycol, neopentyl glycol, p-xylene glycol, 1,4-cyclohexanedimethanol, bisphenol A, p, p'-diphenoxysulfone, 1,4-
Bis (β-hydroxyethoxyphenyl) propane, polyalkylene (eg, ethylene, propylene) glycol, p-phenylenebis (dimethylolcyclohexane), and the like can be used.

The above-mentioned polyester can be produced by either a transesterification method in which polymerization is carried out after transesterification reaction or a direct polymerization method (direct polymerization method) in which polymerization is carried out after esterification reaction, and it is produced either continuously or batchwise. be able to. In the production of polyester, a known catalyst can be used for the esterification reaction, the transesterification reaction, the esterification reaction or the polycondensation after the transesterification reaction. Further known heat stabilizers, antioxidants,
Antistatic agent, lubricant, UV absorber, fluorescent brightener, pigment,
Dyes, light-blocking agents, fillers and the like may be added. Although the esterification reaction proceeds without adding a catalyst, the reaction can be efficiently performed by using the following catalyst. For example, as a catalyst for the transesterification reaction,
Manganese acetate, cobalt acetate, magnesium acetate, calcium acetate, cadmium acetate, zinc acetate, lead acetate, magnesium oxide, lead oxide and the like are generally used. These may be used alone or in combination of two or more. The polycondensation reaction catalyst includes antimony trioxide, antimony pentoxide, antimony trifluoride, antimony sulfide,
Antimony tributyrate, antimony ethylene glycolate, potassium antimonate, antimony acetate, antimony trichloride, germanium dioxide, germanium trioxide, manganese acetate, zinc acetate, lead acetate, alkali metal benzoate, titanium alkoxide (eg, titanium Toxide) and alkali metal salts of titanic acid and the like are generally used. These may be used alone or in combination of two or more.

As a heat stabilizer, phosphoric acid, phosphorous acid or ester compounds thereof may be added. Examples thereof include trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, and mono- or diesters of phosphoric acid or phosphorous acid. Further, known hindered phenols may be added as an antioxidant. For example, commercially available products such as Irganox 1010, Sumilizer BHT, and Sumilizer GA-80 can be used. It is also possible to combine a secondary antioxidant with these primary antioxidants. As the secondary antioxidant, for example, those commercially available under the trade names such as Sumilizer TPL-R, Sumilizer TPM, and Sumilizer TP-D can be used.

The polyester having ethylene-2,6-naphthalate as a main repeating unit used in the present invention is synthesized, for example, as follows. Polyethylene-2,6-
Naphthalate will be described as an example. Polyethylene-
As described above, 2,6-naphthalate is obtained by subjecting dimethyl 2,6-naphthalenedicarboxylate (polybasic acid) and ethylene glycol (polyhydric alcohol) to a transesterification reaction or an ester reaction, and then obtaining an oligomer under vacuum. To perform a polycondensation reaction.

That is, in the transesterification reaction, a polybasic acid and a polyhydric alcohol are reacted at a pressure of 1 to ² kg / cm ² or at atmospheric pressure at 180 to 280 ° C. (preferably 230 to 270 ° C.).
C.) for 0.5 to 8 hours (preferably 2 to 4 hours) to terminate the distillation of the alcohol.
The ester reaction is similarly performed by terminating the outflow of water. Next, the pressure in the tank was reduced to 50 to 1 mmHg and the temperature was raised to 240 to 290 ° C.
The polyester is obtained by heating under a high vacuum of not more than mmHg for a total of 1 to 3 hours. At any stage of the production of the above polyethylene-2,6-naphthalate (preferably before performing the polycondensation reaction), 10 ppm with respect to the polyester from which inorganic fine particles of 0.1 μm or less (eg, colloidal silica, barium sulfate) can be obtained. Or less (preferably 1 to 10 ppm), or a basic compound (eg, sodium hydroxide, potassium hydroxide, quaternary ammonium salt, amines) in an amount of 1 to 100 ppm (preferably 20 ppm). ~ 80p
pm).

The production method of the present invention can be carried out by melt-extrusion using the polyester obtained as described above as follows. This will be described in detail with reference to FIG. FIG. 1 shows a melt film forming apparatus including a melt extruder 1 and a casting roll 8. It was previously dried by heating under reduced pressure (generally 10-250 ° C.
30 hours) Polymer pellets (the surface of which is generally crystallized) are charged into a hopper 2 with a dryer, and the charged polymer is heated and melted in an extruder 3 and is screwed forward (die head 6) by a screw (not shown). Direction). The molten polymer that has passed through the extruder 3 is sent to a filter device (having a filtration filter) housing 4 directly connected to the extruder 3, where it is filtered and then sent to a die head 6. The molten polymer is extruded from a die head 6 onto a casting roll 8 in the form of a sheet, and cooled to produce a polyester film 7. The molten polymer immediately after being extruded from the die head 6 is applied with a voltage of 5 to 15 kV by the electrostatic application electrode 5 and extruded onto the casting roll 8. The obtained polyester film is further transported by the nip roll 9 and wound up by a winding device. Usually, this polyester film is stretched and used for a photographic support or the like. The temperature of the melt extrusion is generally in a range of 270 ° C. to 330 ° C., and the cooling and solidification (that is, the temperature of the casting roll) after the melt extrusion in a sheet shape is preferably performed at 30 to 110 ° C.

The extruder 3 has a pressure gauge P ₁ on the filter device housing side, the filter device housing 4 has a pressure gauge P ₂ , an electric heater (not shown) and a temperature controller T ₂ , and a die head 6. includes a temperature controller T ₃ and an electric heater (not shown). The heating of the filter device housing 4 and the die head 6 is controlled by an electric heater and a temperature controller, respectively. Pressure that appears on the pressure gauge P ₂ is the pressure of the filtration device housing 4, the pressure actually exerted on the filter is connected to the outlet side of the filter housing from the pressure displayed on this P ₂ die head This is the value (pressure loss of the filter) obtained by subtracting the pressure loss of the filter. In the present invention, it is preferable to perform the filtration at a rate of 10 to 50 cm / hour. If the filtration is performed at a speed exceeding 50 cm / hour, there is a problem that the filter is damaged or the captured foreign matter passes through the filter.

In the filter housing 4, for example, FIG.
Is installed. In order to make the configuration easy to understand, FIG.
And FIG. Arrow 20 indicates the direction of movement of the molten polymer, and the molten polymer is introduced from inlet 21. The introduced polymer travels around the conical cone 22 and passes through a disc-shaped filter element 23, 24, 25, 26, 27 having a filter according to the invention (having a central hole). The molten polymer that has passed through the filter element
Center shaft 30 having a flow path inside from a central hole
To the outlet 29 of the filtration device in the direction of arrow 28. Two or more such filtration device housings can be connected. When two units are connected, a method of filtering coarsely with the first unit (that is, using a filter with a slightly larger pore size) and filtering densely with the second unit (that is, using a filter with a smaller pore size) is a method of rapidly and accurately filtering. It is advantageous to perform

FIG. 5 is a sectional view showing the internal structure of the disc-shaped filter element. A filter 51 is installed around a wire mesh 52 via a punching metal 53. Molten polymer is introduced from the direction of arrow 54 and passes through filter 51.

According to the present invention, there is provided a heat-resistant fiber filter having a mesh size of 1 to 20 μm and a porosity of 50 to 90%. Use at least one smaller filter. In the filter of the present invention, a wire mesh as a pre-filter or a filter support is generally placed at least on the side of the filter where the molten polyester enters. As a configuration of the filter element, as shown in FIG. 6, a coarse (ie, large opening) wire mesh 61 and a dense (ie, small opening) wire mesh thereon.
Wire mesh 62, on which the filter 6 of the present invention is placed.
3, and a configuration in which coarse wire meshes 64 are sequentially stacked on the filter is preferable. The coarse wire mesh 61 is the inflow side of the molten polyester, and the coarse wire mesh 64 is the discharge side of the polymer. The coarse wire mesh 61 preferably has a mesh size of about 10 to 200 meshes, and the dense wire meshes 62 and 64 preferably have a mesh size of about 200 to 500 meshes. The assembled cross-sectional view of the filter element of FIG. 6 is shown in the partial enlarged view of FIG. 5 (the part surrounded by a circle).

The filter of the present invention has an aperture of 1 to 20 μm.
m (preferably 1-15 μm) and a porosity in the range 50-90% (preferably 60-90%).
The heat-resistant fiber filter has a smaller pore diameter from the inflow side to the discharge side of the molten polyester. Also, the pore size distribution includes at least a range of 5 to 20 μm (preferably a range of 3 to 20 μm), and its maximum range is generally in a range of 1 to 300 μm;
It is preferably in the range of 1 to 200 μm. FIGS. 7, 8 and 9 show configuration examples of the filter of the present invention. FIG. 7 shows a cross-sectional view of an example of the filter of the present invention. The cavity 7a near the surface of the filter on the molten polyester inflow side has a cavity having a large hole diameter, and the hole diameter near the center 7b is smaller than that on the inflow side. In the vicinity of the center 7c on the molten polyester discharge side, the region again becomes a region where the hole diameter of the cavity is large (the inflow is almost the same as the vicinity), and in the region 7d near the molten polyester discharge side, the hole diameter of the cavity is the smallest. The filter is made of a fine stainless steel wire. The wire diameter is larger as the hole diameter of the cavity is larger, and is smaller as the hole diameter is smaller. FIG. 8 shows a cross-sectional view of another example of the filter of the present invention. There is a cavity having a large pore diameter near the surface 8a of the filter on the molten polyester inflow side, and the pore diameter is small near the center 8b. Then, on the molten polyester discharge side 8c, the region again becomes a region where the hole diameter of the cavity is large, and the hole diameter of the cavity near the molten polyester discharge side is almost the same as that near the inflow side. FIG. 9 is a sectional view of another example of the filter of the present invention. The cavity 9a near the surface of the filter on the molten polyester inflow side has a cavity with a large hole diameter, and the hole diameter near the center 9b is smaller than that on the inflow side. In the vicinity of the center 9c on the molten polyester discharge side, the region again becomes a region where the hole diameter of the cavity is large (the inflow is smaller than in the vicinity), and in the region 9d near the discharge side of the molten polyester, the hole diameter of the cavity is smallest.

The heat-resistant fiber used as the material of the filter of the present invention is preferably a metal fiber or a ceramic fiber, and particularly preferably a metal fiber (eg, stainless steel).

As described above, the filter of the present invention generally comprises a region having a large pore size on the inflow side of the molten polyester and a region having a small pore size inside the region. That is, in the filter of the present invention, at least a region having a large pore size on the inflow side of the molten polyester and a region having a small pore size inside the region may be provided. Regions can be added. The region of large pore diameter on the inflow side is 20 to
A region having a pore size distribution including the range of 50 μm and being in the range of 10 to 200 μm, and a small pore size region inside the region having a pore size distribution of at least 3 to 10 μm and 1
It is preferable that the region has a pore size distribution in the range of ５０50 μm. Also, if the filtering device has an aperture of 1
A filter of a heat-resistant fiber having a pore size in the range of 50 to 90% and a pore size decreasing from the inflow side to the discharge side of the molten polyester; ２０20 μm,
It is preferable to have a filter of heat-resistant fiber having a porosity in the range of 50 to 90% and two filters. The filter having an aperture of 1 to 5 μm preferably has a pore size distribution including at least the range of 1 to 5 μm and within the range of 1 to 20 μm, and the aperture of 6 to 20 μm.
It is preferable that the pore size distribution includes at least a range of 5 to 20 μm and is in a range of 1 to 200 μm. Further, the configuration shown in FIG. 7, FIG. 8 or FIG. 9 may be composed of two filters.

The polyester film obtained in the present invention is usually further subjected to a stretching treatment for use as a support for a silver halide photographic film, for example. In general, the support for a photographic film is preferably a biaxially stretched polyester film (biaxially stretched polyester film). The polyester film obtained by the method of the present invention is stretched 2 to 5 times in the longitudinal direction (long direction) and in the horizontal direction (width direction) at a temperature of 120 ° C to 160 ° C, and then 165 times. The biaxially stretched polyester can be obtained by performing the heat treatment at 290 ° C.

[0026]

EXAMPLES The method for producing a resin in the present invention will be described below with reference to specific examples, but the present invention is not limited thereto.

[Embodiment 1] A description will be given with reference to FIGS. A polymer hopper of polyethylene-2,6-naphthalate (the surface of which has been crystallized) previously heated and dried at 175 ° C. for 14 hours under reduced pressure is supplied to a hopper 2 with a dryer.
To The injected polymer is 305 in the extruder 3.
And heated and melted at ℃, and a screw (screw diameter: 40 m
m) and is sent forward (toward the die head 6). Extruder 3
Is sent to a filtration device (having a filtration filter) housing 4 directly connected to the extruder 3,
After being filtered here, it is sent to the die head 6. The filter shown in FIG. 2 is installed in the housing 4, and five filter elements (see FIG. 5) constituting the filter are provided with five 3-inch leaf desks (filtration area: 250 cm ² ) (FIG. 2). 23, 24, 25, 26, 2
7). As shown in FIG. 6, the structure of the filter element is a 60-mesh wire mesh 61, a 210-mesh small wire mesh 62, a filter (filter media) 63 on the wire mesh 62, and a coarse mesh on the filter. Has a configuration in which the metal nets 64 are sequentially stacked.

The filter has the structure shown in FIG. 7 and is as follows (FIG. 7 is a copy of an enlarged sectional photograph of the filter). Aperture: 5 μm Pore size distribution: 20 to 200 μm for 7a, 10 to 10 for 7b
0 μm, 7c is 5 to 50 μm, 7d is 3 to 10 μm, porosity: 86%, thickness: 0.85 mm, material: stainless steel

Die head (width: 150 mm, lip width:
2 mm) 6, the molten polymer was extruded at 305 ° C. onto a casting roll 8 having a surface temperature of 70 ° C. in the form of a sheet, and cooled to prepare a polyester film 7. The molten polymer immediately after being extruded from the die head 6 was applied with a voltage of 10 kV by the electrostatic application electrode 5 and extruded onto the casting roll 8. Obtained polyester sheet (thickness: 0.9 mm, width: 1)
50 mm) was further transported by the nip roll 9 and wound up by a winding device. The linear speed (filtration speed) at which the molten polymer was sent out was 30 cm / hour, and the pressure of the filter was 97 kg / cm ² .

[Example 2] In Example 1, the filtration was carried out in the same manner as in Example 1, except that two filtration device housings were directly connected and connected as the filtration device housing 4. Thus, a polyester film was produced. The filter elements used for the two housings had the same configuration except that the following filter was used. The filter of the filter element on the extruder side has the configuration shown in FIG. 8 and is as follows (FIG. 8 is a copy of an enlarged sectional photograph). Aperture: 10 μm Pore size distribution: 8a is 50 to 200 μm, 8b is 20 to
100 μm, 8c is 5 to 50 μm, porosity: 86%, thickness: 0.75 mm material: stainless steel The filter of the filter element connected above has the configuration of FIG. 9 and is as follows (FIG. 9). Is a copy of the enlarged cross-sectional photograph). Aperture: 3 μm Pore size distribution: 9a is 20 to 200 μm, 9b is 10
100 μm, 9c is 5 to 50 μm, 9d is 1 to 5 μm
m, porosity: 85%, thickness: 0.85 mm, material: stainless steel, the linear speed (filtration speed) for sending out the above molten polymer is 2
0 cm / hour and the pressure of the filter was 127 kg / cm ² .

Comparative Example 1 The same procedure as in Example 1 was repeated except that the following filter was used as a filter for the filtration device housing, and the mixture was extruded in the same manner as in Example 1 to produce a polyester film. The configuration of the filter is as follows. Aperture: 5 μm Pore size distribution: 10 to 200 μm (no change in the thickness direction) Porosity: 76% Thickness: 1.0 mm Material: Stainless steel The linear speed (filtration speed) of the molten polymer is 3
0 cm / hour and the pressure of the filter was 151 kg / cm ² .

The obtained polyester film was evaluated as follows. (1) Number of Foreign Substances The polyethylene-2,6-naphthalate films obtained in Examples and Comparative Examples were cut into squares each having a side of 10 cm, and were vertically and horizontally tripled at 135 ° C. and 1 m / min. The film was stretched at a speed to produce a biaxially stretched polyester film having a thickness of 90 μm. Stretching is long (TM Long)
This was performed using a stretching machine manufactured by the company. The above stretched film,
The sample was cut into a size of 10 cm × 20 cm, and foreign matters forming voids (voids) were observed with an optical microscope equipped with a polarizing plate. Then, the type of foreign matter was selected, its size was measured, and the number of each was counted. However, regarding the type of foreign matter, the color of the polarizing plate was confirmed, and black foreign matter and other foreign matter (referred to as colored foreign matter other than black) were separated. The larger and larger the black foreign matter, the more the black foreign matter hinders image formation. In addition, other foreign substances, for example, brown foreign substances transmit light, so it is difficult to hinder image formation as described above as compared to black foreign substances,
It may be caused by thermal degradation of the polymer, which causes slag and die streaks. And these occurrences
In many cases, spot defects are provided inside the obtained film. The size of the foreign substance is measured on a television monitor using a CCD camera and an image processing device attached to the microscope. In each of the samples, the number of foreign substances was indicated in terms of 100 μm in thickness and 1 cm ² . (2) pressure on the pressure filter according to the filter from the value of the pressure gauge P ₂ of the filter, and displayed as a value obtained by subtracting the pressure loss of the die head that is connected to the filter outlet side (pressure loss of the filter).

Further, the aperture (hole diameter) was determined by the following method. 1) A filter (filter medium) is cut into a circular shape having a diameter of 20 mm, and 100 to 200 ml of a simulation liquid in which polystyrene-based standard particles are dispersed in water in an amount of 100 to 500 ppm is passed through the circular filter. 2) To the filtrate passed through the filter, a small amount of polyvinyl alcohol was added and mixed, and then 0.5 ml of the polyvinyl alcohol was dropped on an aluminum plate, and heated to dryness at about 60 ° C. under normal pressure to obtain an aperture. A sample for measurement was prepared. 3) The sample is photographed with an electron microscope (SEM), and the photograph is taken into an image processing system equipped with a CCD camera, and the standard particle density (the number of particles of each particle diameter per unit area) is calculated. 4) With respect to the simulated liquid that does not pass through the filter, the above processes 2) to 3) are performed, and the standard particle density is calculated.
Used as a reference. 5) As the simulated liquid, several kinds of standard particles (for example, particles having a particle diameter (diameter) of 0.5 μm, 1.0 μm, 2.1 μm,
A particle obtained by simultaneously dispersing 5 to 10 kinds of particles having a particle size close to the value, such as 3.2 μm and 5.2 μm, in water is used. 6) The following formula (1) for particles of each particle size in the simulated liquid.
The particle size of the particles having a particle collection rate of 100% represented by 表 was defined as the aperture.

The pore size distribution is obtained by taking a photograph of a cross section of a filter or a wire mesh, taking the photograph into a personal computer equipped with a CCD camera, and examining the shape of the hole surrounded by fibers (generally a polygonal shape. The distribution was measured by considering the long side (longest) for triangles and squares, and the longest diagonal for pentagons and above as pore diameters. The measurement is performed at 500 to 1000 locations.

The results of the above evaluation are shown in Table 1 below.

[0036]

[Table 1] Table 1 ──────────────────────────────────── Filter configuration Linear velocity filter Number of foreign substances Pressure Black / Others Pore size Porosity Pore size (cm / hr) (kg / cm ² ) 5-10 10-20 20-30> 30 (μm) (%) Change (μm) ───────────実 施 Example 1 75 provided 30 97 5/1 2/0 0/0 0/0 Example 2 75 provided 20 127 1/1 2/0 0/0 0/0 ──────────────────────────────────── Compare Example 1 75 None 30 151 9/1 6/2 1/1 0/0 ──────────────────────────────── ────

[0037]

According to the method for producing a polyester film of the present invention, it is possible to produce a polyester film containing polyethylene naphthalate as a main component from which fine foreign substances have been highly removed, with high productivity. That is, by utilizing the filtration method of the present invention during melt extrusion of PEN,
At a relatively high speed at which the polymer is not deteriorated, fine particles having a size of 20 μm or less can be removed and filtered. Therefore, the PEN film in which the amount of minute foreign matter is reduced is
As with ET, it can be obtained with high productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a melt film forming apparatus including a melt extruder and a casting roll that can be used in the production method of the present invention.

FIG. 2 is a cross-sectional view of the filtration device installed in the filtration device housing of FIG.

FIG. 3 is a perspective view showing an assembling process of the filtration device of FIG. 2;

FIG. 4 is another perspective view showing an assembling process of the filtration device of FIG. 2;

FIG. 5 is a sectional view showing an internal structure of the disc-shaped filter element of FIG. 2;

FIG. 6 is a schematic diagram showing an example of a configuration of a filter element including a filter used in the present invention.

FIG. 7 is a copy of a cross-sectional photograph of an example of a filter used in the present invention.

FIG. 8 is a copy of a cross-sectional photograph of another example of a filter used in the present invention.

FIG. 9 is a copy of a cross-sectional photograph of another example of a filter used in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Melt extruder 2 Hopper with dryer 3 Extruder 4 Filtration apparatus housing 5 Electrostatic application electrode 6 Die head 7 Polyester film 8 Casting roll 9 Nip roll 20, 28 Arrow 21 Inlet 22 Conical cone 23, 24, 25, 26, 27 Disc-shaped filter element 29 Outlet 30 Center shaft 51 Filter 52 Wire mesh 53 Punched metal 54 Arrow 61, 64 Coarse wire mesh 62 Dense wire mesh 63 Filter

Claims (5)

[Claims] 1. A method for producing a polyester film, comprising melting a polyester in which 70 to 100 mol% of all repeating units are 2,6-ethylene naphthalate units, filtering the mixture, and extruding the resultant into a sheet. The filtration is performed using a heat-resistant fiber filter having an opening in the range of 1 to 20 μm and a porosity in the range of 50 to 90%, and a pore size of the void from the inflow side to the discharge side of the molten polyester. A method for producing a polyester film, wherein the filtration is performed using at least one filter having at least one filter that changes so as to reduce the size. 2. The method for producing a polyester film according to claim 1, wherein the opening is in a range of 1 to 15 μm. 3. The method for producing a polyester film according to claim 1, wherein the porosity is in the range of 60 to 90%. 4. The method according to claim 1, wherein the heat-resistant fiber is a metal fiber. 5. The method for producing a polyester film according to claim 1, wherein the repeating unit other than the 2,6-ethylene naphthalate unit of the polyester is an ethylene terephthalate unit.