JP2001089590A - Method for producing polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing, in a good productivity, polyester film where a film surface is hardly fouled and surface properties are excellent. SOLUTION: This method for producing the polyester film comprises removing low molecular weight substances existing on the film surface be at least one surface treatment selected from the group consisting of solvent treatment, corona discharge treatment, plasma arc treatment and flame treatment in a step between a cooling/solidifying process and a longitudinally drawing process in producing the polyester film by extruding polyester from a slit-like nozzle, cooling/solidifying it and longitudinally drawing solidified film.

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 high-quality polyester film having a minimum amount of oligomer stains and surface scratches at the time of film formation with high productivity by removing as much as possible low molecular weight dirt on the polyester film surface. Things.

[0002]

2. Description of the Related Art Conventionally, polyesters, particularly polyethylene terephthalate, are relatively inexpensive, but have excellent transparency, chemical resistance, mechanical strength, heat resistance, gas barrier properties, and the like, so that they can be used as base materials for magnetic recording media. For electrical insulation of films, capacitors, etc., OA for printer ribbons, etc.
It is used for applications and materials for beverage containers.

[0003] However, in polyethylene terephthalate, oligomers including ethylene terephthalate cyclic trimer (hereinafter, cyclic trimer) are usually 0.6 to 1.
About 4% by weight, such oligomers diffuse into the air when they are released into the air at a high temperature in the extrusion process of the film, or ooze out of the film, and cause And casting drums,
Or because it causes stains on the roll and film itself,
This is transferred to the polyester film product,
For example, in the case of a magnetic tape, a defective product such as a reading error is caused, and a trouble such as deterioration of quality is caused.

[0004] For this reason, the quality of the roll is often maintained by cleaning the surface of the roll, and this leads to a decrease in productivity, which has been regarded as a problem.

[0005] To deal with such a problem of contamination, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 101462 describes that oligomers that bleed out due to special heating such as heating under reduced pressure are reduced in a series of film forming steps. In addition, there are known approaches from the raw material stage where it is difficult to produce cyclic oligomers.However, these methods have problems of lowering productivity and increasing costs, and all of them have problems on the surface during melt extrusion. The amount of oligomers adhering can be reduced but cannot be completely removed, and it is still not enough to prevent the accumulation of dirt on the roll.

[0006]

SUMMARY OF THE INVENTION In view of the background of the prior art, an object of the present invention is to provide a method for producing a polyester film having less stain on the film surface and excellent in surface properties with high productivity. .

[0007]

The present invention employs the following means to solve the above-mentioned problems. That is, in the method for producing a polyester film of the present invention, in a method of extruding from a slit-shaped die, cooling and solidifying, and then longitudinally stretching to produce a polyester film, a step between the cooling and solidifying step and the longitudinal stretching step Wherein the low molecular weight substances present on the film surface are removed by at least one kind of surface treatment selected from a solvent treatment, a corona discharge treatment, a plasma discharge treatment and a flame treatment.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is directed to the above-mentioned subject, that is, a polyester film excellent in surface characteristics with little stain on the film surface and having no scratches. When the product (hereinafter, oligomer) extrudes the film from the die, it slightly remains on the film surface, accumulates on the roll, and grows into stains that leave scratches on the film. Find out what is causing
Furthermore, the inventors have sought to solve such a problem at once by treating the film surface to remove such stains, that is, oligomers on the cast film before the first stretching step (longitudinal stretching step). is there.

The surface treatment of the film in the present invention means at least one treatment selected from a solvent treatment, a corona discharge treatment, a plasma discharge treatment and a flame treatment. Such a surface treatment may be a single treatment alone, but it is preferable to perform a plurality of treatments in an overlapping manner so that the surface treatment can be more effectively removed.

[0010] In the solvent treatment, the cast film is subjected to a washing treatment by passing it through a washing tank filled with a solvent. As the solvent for the solvent treatment, at least one selected from water and alcohol, preferably ethanol, is preferably used. In such a solvent treatment, it is preferable to continuously apply ultrasonic vibration to the solvent solution. By exciting such ultrasonic vibration,
Oligomers on the film surface can be more thoroughly washed away. After the solvent treatment, further washing is performed with a shower-like washing liquid (solvent) in the air in order to wash away the re-adhered oligomer, and finally drying is performed by blowing dry air with an air knife or a dryer. Is preferred.

That is, by performing such a surface treatment, oligomer stains adhered to the film during extrusion can be washed out, preferably at most 3.0 ng / cm ² , more preferably almost completely.

[0012] Corona discharge treatment, which is one of such surface treatment methods, is known as a technique for improving the wettability of a polymer. Corona discharge treatment is a process in which a material to be treated is sandwiched between a pair of electrodes in an atmospheric pressure state, a high AC voltage is applied between the two electrodes to excite the corona discharge, and the surface of the material to be treated is exposed to the corona discharge. Therefore, it is known as a technique for modifying the surface state of a material to be treated. As useful gases for generating such corona, mainly He, A
r, N ₂ , CO, CO ₂ , O _2, or a mixed gas thereof can be used. If this kind of corona discharge treatment is applied to the polymer, the main chain of the resin on the surface can be cut off, and in the case of the polymer, the adhesiveness can be improved. However, in the present invention,
Such an effect of improving the adhesiveness is rather a hindrance to the film surface, that is, it is not preferable because the film sticks to the roll surface in the longitudinal stretching step. Accordingly, the present invention provides a method for treating such a corona discharge treatment within a short time to such an extent that the effect of improving the adhesiveness is not caused, thereby decomposing only the low-molecular-weight substances present on the film surface and effectively reducing the oligomer. Is to be removed.

In other words, when the shape of the object to be treated is uniform and extremely small, the discharge time may be instantaneous, and when the shape is large, the object to be treated is run at a higher speed or a corona discharge is performed. A method of running the processing electrode at a high speed can be adopted. In the film production line,
The object to be processed is a running film, but the speed is slow, and such a means cannot prevent the surface modification of the film. For example, a corona discharge nozzle is swept at high speed in parallel with the film to be processed. Thereby, the oligomer can be effectively removed.

[0014] The film can also be cleaned by plasma discharge treatment. The plasma referred to here is composed of a group of electrons having a large number of atoms ionized and having negative electricity and a group of ions having a positive charge.
In many cases, plasma discharge is due to glow discharge, and can generate active species higher than corona discharge at a low pressure of about 0.001 to 0.01 Torr. However, since such plasma processing is performed in a vacuum system, continuous processing is difficult, and productivity is extremely poor, and the equipment itself becomes large.

Therefore, microwaved glow discharge plasma or the above-mentioned corona discharge is generated between the discharge electrode and the object to be processed at normal temperature and atmospheric pressure, and is generated under the atmospheric pressure (normally) by the strong electric field generated. A mode in which plasma is generated at about 760 Torr is preferably used.

These surface treatment methods are characterized in that only oligomers on the surface of the treated material are decomposed and removed, no harmful substances remain, and the temperature rise is extremely low. In the above-mentioned processing method, although not particularly limited, adopting a method of coating and treating the discharge electrode with a dielectric material can reduce spark at the discharge electrode and reduce processing unevenness. It is possible and preferable. As such a dielectric material, a fluororesin or a silicon resin is preferably used.

Next, a flame (flame) treatment, which is one of such surface treatment methods, is preferably employed because only deposits on the film surface can be removed in the same manner as in the surface treatment. As the frame processing method,
A method of performing a surface treatment using a frame processing device manufactured by Clean Burner or a frame processing device manufactured by esseCI is preferably used. Also in this processing method, it is necessary to run the front end of the frame processing at a high speed in parallel with the film as in the case of the electric surface processing.

Further effects are desired by combining some of the above surface treatments. Preferably, a combination of plasma discharge treatment and ultrasonic cleaning may have a high effect.

In addition to the surface treatment method of the present invention, by combining a means for adding an aliphatic ester or the like to the raw material, even after the oligomer on the film surface is removed, the bleed out of the oligomer can be prevented. Is minimized, so that a film with less stain can be finally provided.

As the polyester resin in the present invention, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, poly-1,4-cyclohexane dimethylene terephthalate and the like can be used. In particular, polyethylene terephthalate is inexpensive, so it is used in a wide variety of applications and is highly effective. Further, these resins may be homo resins, or may be copolymers or blends.

When the polyester film used in the present invention is polyethylene ethylene terephthalate, it is preferable that the polyester film contains 85 mol% or more, preferably 95 mol% or more of the total amount.

In the case of polyethylene terephthalate, the polyester used in the present invention can be produced by a conventionally known production method. That is, terephthalic acid and ethylene glycol and, if necessary, a copolymerization component are directly reacted to distill off water and esterify the mixture, followed by polycondensation under reduced pressure, or dimethyl terephthalate and ethylene glycol as necessary. , The methyl alcohol is distilled off, the ester exchange is carried out, and then polycondensation is performed under reduced pressure. Solid-state polymerization may be performed to further increase the intrinsic viscosity and reduce the content of cyclic trimers and acetaldehyde. The melt polycondensation reaction,
The reaction may be performed in a batch reactor or a continuous reactor. In any of these methods, the melt polycondensation reaction may be performed in one stage or may be performed in multiple stages. The solid-state polymerization reaction can also be performed in a batch-type apparatus or a continuous-type apparatus, similarly to the melt polycondensation reaction. The melt polycondensation and the solid phase polymerization may be performed continuously or separately.

The polyester resin used in the present invention may be provided with a colorant, an ultraviolet absorber, an antioxidant, an antistatic agent, a lubricant, a nucleating agent, a release agent, etc., if necessary, without impairing the object of the present invention. It can be added in a range.

In the case of the above polyester film,
You may shape | mold as follows. Polyester is supplied from a hopper, melt-kneaded by a screw in an extruder, and sent to a die. If necessary, foreign matter may be removed via a filter, or a gear pump may be provided to improve supplyability. After being formed into a sheet through a die, it is preferably discharged and cooled and solidified on a mirror-plated chrome-plated drum, and formed into a film. At this time, a method is preferably used in which static electricity is applied to the sheet-like molten resin, the sheet-like molten resin is brought into close contact with the drum, and rapidly cooled and solidified. The cast film thus obtained is biaxially stretched at a temperature equal to or higher than the glass transition temperature, whereby oriented crystallization occurs, and a tough film excellent in mechanical strength and heat resistance is preferably obtained. The stretching ratio can be selected according to the strength and thickness of the application,
The product of the longitudinal and transverse stretching ratios is preferably about 2 to 30 times. The film biaxially stretched by such a production method is heat-set in a tenter at a temperature equal to or higher than the stretching temperature and equal to or lower than the melting point in order to impart flatness and dimensional stability, and is cooled to room temperature and wound.

Oligomer contamination which is a problem in a die, a casting drum, a longitudinal stretching roll, etc. is mainly composed of an oligomer having a highly volatile linear structure (hereinafter referred to as a linear oligomer). Is what is done. Therefore, by suppressing the linear oligomer component on the film surface, it becomes possible to significantly reduce such device contamination. Therefore, the ratio of the linear oligomer contained in the extracted oligomer on the film surface is preferably 30% by weight or less, and if it exceeds 30% by weight, the oligomer stain on the roll becomes severe, Frequent cleaning is required, which is not preferable.

Here, the linear component in the extracted oligomer is mainly a monomer represented by terephthalic acid (hereinafter, TPA), monohydroxyethyl terephthalic acid (hereinafter, MHT), bishydroxyethyl terephthalic acid (hereinafter, BHT) and the like. In addition, there are dimers and trimers (oligomers) in which ethylene terephthalate is present linearly as a repeating unit two to four times and has a carboxylic acid or a hydroxyl group in a terminal group. The linear oligomer has a sublimation point lower than that of the cyclic component, and contains a large number of those which easily evaporate and volatilize at the film forming temperature.

The polyester cast film provided by the method of the present invention is characterized in that the amount of oligomer attached on the film surface is small. That is, the amount of the extracted linear oligomer on the film surface is preferably 3.0 ng /
A low level of not more than cm ² , more preferably not more than 1.5 ng / cm ² , particularly preferably not more than 1.0 ng / cm ² , is preferable from the viewpoint of prevention of fouling of a casting drum or a roll. Such a film having a small amount of extracted linear oligomers can make these devices less likely to be contaminated when contacting devices such as drums and rolls at the time of film formation, and further reduce device contamination such as drums and rolls. For this reason, scratch defects on the film surface can be suppressed. On the other hand, in the case of a film in which the amount of the extracted linear oligomer on the film surface exceeds 3.0 ng / cm ² , after 10 hours from the start of the film formation, the oligomer stain is noticeable on the roll. Therefore, the above-described various problems occur.

In order to control the amount of oligomer on the film surface, it is preferable that the heating temperature of the polyester film in the melting portion in the extruder is equal to or higher than the melting end temperature of the polyester resin and lower than the thermal decomposition starting temperature. If the melting temperature is lower than the melting end temperature, unmelted matter remains in the polyester resin, and the filter pressure of the polymer increases due to clogging in the filter and an increase in melt viscosity, which undesirably promotes the generation of oligomers. Further, even when the temperature is equal to or higher than the thermal decomposition starting temperature, a similar problem occurs because a thermally degraded polymer is generated.

[0029]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples.

The methods of evaluating and measuring the physical properties used in the examples are according to the following methods. (1) Amount of extracted oligomer on polyester film surface From the obtained unstretched film, 4.5 cm × 4.5 cm
Cut out 15 square samples. Next, a beaker containing 50 ml of ethanol for extraction is placed in an ultrasonic cleaner containing water, and the samples are subjected to ultrasonic treatment one by one for 90 seconds. After concentrating the filtrate, chloroform was added, acetonitrile was added, and the volume was adjusted.
The amount of cyclic trimer was quantitatively analyzed by liquid chromatography. In addition, TPA, MHT, which are linear oligomers,
BHT removes the solvent from the solution with a nitrogen purge,
The redissolved substance in acetonitrile was quantified by liquid chromatography. The analysis conditions are as follows.

HPLC analyzer: Shimadzu Corporation
Pump (LC-6A): Shimadzu Corporation System controller (SCL
-6A): Shimadzu Corporation UV detector (SPD-6AV) Column: INTERSI manufactured by Gaschrom Corporation
L ODS-24.6 × 250
mm Developing solvent: A = pure water, B = acetonitrile Flow rate: 1.5 ml / min Wavelength: 242 nm Column temperature: 45 ° C. For quantification, use a standard curve of each oligomer whose concentration is known in advance. It was prepared and quantified from the peak area of the HPLC chromatogram. The amount of oligomer in the whole extract was calculated from the amount of oligomer obtained, and the amount of oligomer per unit volume was converted from the total area of the extracted film. (2) Roll dirt The oligomer dirt on the roll is cleaned thoroughly with the longitudinal stretching roll before the start of film formation, and the stain state 10 hours after the start of the film formation is visually observed, and is not different from that before the film formation. ◎ indicates a clean thing, ○ indicates that there is almost no dirt at first glance, 薄 く indicates that the dirt can be confirmed very thinly, but does not cause any problem, Those requiring replacement were evaluated as "x". (3) Film surface scratches The film is actually formed, and a cast film after 10 hours and a uniaxially stretched film after longitudinal stretching are collected, and the films are respectively observed by transmitted light. At this time, a 5 m long film surface was observed for a 50 cm wide cast film, and a 20 m long film surface was observed for a uniaxially stretched film of the same width. Furthermore, in the case of a biaxially stretched film having a width of 165 cm, which was subjected to transverse stretching and heat treatment with a tenter, a 20 m length was taken, and the number of surface flaws that could be visually confirmed was also measured. When the number of surface scratches is 10 or more, respectively, "x" indicates that the surface cannot be used, and 3 to 9 indicates that the surface is considerably deteriorated, but "" indicates that the surface can be used.
"O" indicates that the surface quality is good with 2 scratches and almost no scratches.
The case where no flaw was observed was evaluated as “◎”. The surface scratches after the surface treatment shown in Table 2 represent the scratches of the sample after removing the oligomer of the film in each example, and the surface scratches after the uniaxial stretching represent the scratches of the sample after the longitudinal stretching. The surface scratches after biaxial stretching represent scratches of the sample that was stretched in the longitudinal direction and then further stretched in the transverse direction. Examples 1-3 Polyester terephthalate of IV = 0.62 deciliter / g obtained by continuous polycondensation was used. This polyethylene terephthalate was vacuum-dried at 180 ° C. for 3 hours, sent to a melting section from a hopper of an extruder, melted and kneaded at 280 ° C., and then sent to a measuring section. At this time, the discharge amount of the molten polymer was kept constant at 100 kg / hr. Thereafter, the molten resin is sent to the T-die via a filter by a gear pump. Next, a sheet-like unstretched film having a thickness of 120 μm was obtained by cooling and solidifying the sheet-like molten material extruded from the T-die on a mirror chromium plating kept at 25 ° C. by applying electrostatic force of 8 kV.

The unstretched film was ultrasonically oscillated at a frequency of 36 kHz for 10 seconds or 60 seconds through a water bath filled with water or ethanol. Table 1 shows the conditions. Thereafter, the cyclic trimer oligomer and linear oligomer contained per square cm on the film surface were evaluated. The results are shown in Table 2.

The obtained cast film was guided to a stretching roll and stretched 3.3 times in the machine direction at 95 ° C. to obtain a uniaxially stretched film.

Further, the uniaxially stretched film is guided to a tenter and both ends are clipped, and the film is stretched in the transverse direction so as to be perpendicular to the longitudinal stretching direction. Stretching temperature is from 90 ° C to 95
The film was heat-set at 230 ° C., and the film was relaxed at 90 ° C. to obtain a biaxially stretched film.

The unstretched film, the uniaxially stretched film and the biaxially stretched film were sampled 10 hours after the film was formed, and the surface damage was evaluated. Table 2 shows the results. Example 4 On an unstretched film obtained in the same manner as in Example 1, three corona discharge nozzles equipped with a high-speed movable arm were disposed vertically and three times in the width direction to discharge. The distance from the tip of the nozzle to the film surface was 50 mm. The corona discharge treatment speed at this time also took into account the speed in the direction opposite to the film running direction, and the relative speed was kept constant at 150 m / min. The corona discharge treatment machine is manufactured by VETAPHONE and its output is 2.6
KW. Note that air was used as a corona generating gas. Tables 1 and 2 show the corona discharge conditions and the evaluation of the corona-discharged film, respectively. Example 5 An unstretched film obtained in the same manner as in Example 1 was added to Example 4
1. With a plasma processing device (manufactured by AGRODYN) arranged in the same manner as above, the relative speed is 150 m / min on both sides, and the output is 2.
The polyester film subjected to the plasma discharge treatment at 8 kW was evaluated. The conditions and results are shown in Tables 1 and 2.
Note that air was used as the generated gas. Example 6 An unstretched film obtained in the same manner as in Example 1 was added to Example 4
Frame processing equipment (made by esseCI)
A polyester film having both sides subjected to a frame treatment at a processing speed of 100 m / min was evaluated. The conditions and results are shown in Tables 1 and 2.

[0036]

[Table 1]

[0037]

[Table 2]

As is clear from the results shown in Table 1, Examples 1 to 3 were subjected to ultrasonic cleaning through water or ethanol.
In (3), almost all of the cyclic oligomer can be removed. Furthermore, the total amount of linear oligomers causing process fouling has been reduced to 3.0 ng / cm ² or less. It can be seen from Examples 1 and 2 that the effect of this reduction is further reduced by increasing the treatment time, as shown in Examples 1 and 2, and that the effect is higher when the solvent is ethanol. Further, almost no oligomer contamination on the stretching roll after ultrasonic cleaning was observed, and no surface scratches due to the oligomer were observed on the obtained cast film. Even in the uniaxially stretched or biaxially stretched film, although there were some scratches, it was of a degree that would not hinder use at all.

In Examples 4 to 6 in which the film was subjected to various surface treatments, the amount of the cyclic oligomer extracted from the surface of the obtained cast film was 2.88 ng / cm ² or less, which was reduced to about 1 to 3 in Examples. Although not found, the amount of linear oligomers, which is the main cause of roll fouling, was further reduced to 1.0 ng / cm ² or less. Further, in the obtained cast film, no damage due to electric discharge treatment or flame treatment was observed. Particularly, in Example 5 by the plasma treatment, almost no oligomer contamination on the roll was observed, and no surface scratches due to the oligomer were observed on the cast film. No surface damage was observed in the uniaxially stretched or biaxially stretched film, and a high-quality film was obtained. Comparative Example 1 A film was formed using the same PET resin as in Example 1. Further, the discharge amount of the polymer, the casting conditions and the uniaxial stretching conditions were the same as in Example 1. However, no treatment was applied to the cast film, and uniaxial stretching and biaxial stretching were performed under the same conditions as in Example 1.

In Comparative Example 1 in which the sample was untreated (no surface treatment) after casting, as shown in Table 2,
Among the extracted oligomers on the surface, the amount of cyclic oligomer is
23.2 ng / cm ^{2, which} is extremely large, and the amount of linear oligomer is
It was contained as much as 6.7 ng / cm ² . It was also observed that white oligomers were attached to the rolls so that they could be easily visually identified. Furthermore, in the obtained uniaxially stretched or biaxially stretched film, many scratches and foreign substances due to oligomers were observed.

[0041]

According to the present invention, the amount of oligomers on the surface of the cast film can be minimized, and a high-quality polyester film free from stretch roll contamination can be provided with high productivity.

 ────────────────────────────────────────────────── ─── front page of continued F-term (reference) 4F071 AA43 AG01 AG16 AG17 AG30 BA01 BB06 BB08 BC01 4F073 AA23 AA25 BA23 BA24 BB01 CA01 CA21 EA03 GA03 4F210 AA24 AE01 AG01 AM27 AM28 AR02 QA02 QA03 QC02 QC06 QD06 QD07 QD10 QG01 QG18 QW07 4J002 CF041 CF061 EH146 4J029 AA01 AA03 AB07 AC01 AC02 AE03 BA03 BA05 BD04A CB06A CC06A HA01 HB01 KH08

Claims (6)

[Claims] 1. A method for producing a polyester film by extruding from a slit-shaped die, cooling and solidifying, and then longitudinally stretching the polyester film, wherein the polyester film is present on the film surface in a stage between the cooling and solidifying step and the longitudinal stretching step. Low molecular weight material,
A method for producing a polyester film, wherein the polyester film is removed by at least one kind of surface treatment selected from a solvent treatment, a corona discharge treatment, a plasma discharge treatment, and a flame treatment. 2. The method according to claim 1, wherein the solvent used in the solvent treatment is at least one selected from water and alcohol. 3. The method for producing a polyester film according to claim 1, wherein ultrasonic waves are applied to the solvent solution in the solvent treatment. 4. The method according to claim 1, wherein the plasma discharge treatment is performed in a range of 0.001 to 76.
The method according to claim 1, wherein the method is performed in an atmosphere of 0 Torr. 5. The polyester film according to claim 1, wherein a low molecular weight substance remaining on the surface of the polyester film after the surface treatment is 3.0 ng / cm ² or less. Production method. 6. The method for producing a polyester film according to claim 1, wherein the low molecular weight product is an oligomer having a linear structure.