JPH10180844A - Polyester film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen stain of oligomer in making a film by lessening oozing out of the oligomer on a film surface by a method wherein an extracted oligomer amount on a surface of a polyester film obtained by a melt extrusion method is specified. SOLUTION: An extracted oligomer amount on a surface of a polyester film obtained by a melt extrusion method is made under 2.0mg/m<2> . Further, the polyester film contains 0.6-1.4wt.% of oligomer content, and a ratio of a linear constituent contained in the extracted oligomer on the film surface is under 30%. Therefore, the polyester film is manufactured by a method wherein after heating once polyester resin at a temperature of a melting end temperature or higher to and excluding a thermal decomposition start temperature in a melt part of an extruder, it is cooled so that a surface temperature of a sheet like melt resin at an outlet of a flat die becomes a temperature of under a melting end temperature down to and including descent temperature crystallization start temperature, and the sheet like melt resin is preferably cooled with the flat die or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high-quality polyester film which has a low leaching of low molecular weight compounds on the film surface, has very few oligomer stains and surface defects during film formation, and has an excellent productivity. It relates to a method of manufacturing under

[0002]

2. Description of the Related Art Polyester films, especially polyethylene terephthalate films (hereinafter referred to as PET films) have been widely used in industrial applications because of their excellent mechanical, thermal, and electrical properties.
Although the demand is increasing, demands for film characteristics and productivity are becoming more severe with the recent expansion of applications and production.

[0003] Above all, there is a serious problem that productivity is hindered by fouling of the apparatus at the time of forming a polyester film and flaws on the surface of the film. There is an increasing demand for the reduction of oligomers).

Particularly, PET generally contains about 0.6 to 1.4% by weight of an oligomer including an ethylene terephthalate cyclic trimer (hereinafter, referred to as a cyclic trimer). In the process of extruding a film, when it is released into the air at a high temperature, it diffuses into the air, or leaches from the inside of the film to the surface, causing stains on the base, casting drum, or film or roll. Therefore, during the production of the polyester film, problems such as a decrease in productivity and a deterioration in quality due to scratches on the film were caused.

In general, when a thermoplastic resin is melted and extruded by an extruder, as the amount of extruded resin increases or the intrinsic viscosity (IV) of the extruded resin increases, the fluid after the extruder or the extruder is increased. During the passage through a pipe, a filter, or the like, the extrusion temperature tends to be higher due to viscous heat generation, and the resin temperature tends to be higher due to shear heat generation as the discharge pressure increases.

Particularly, when a molten resin is kept at a high temperature of not less than a melting point (Tm) + 40 ° C. during a process from an extruder to a die when producing a polyester film, an oligomer which is a decomposition product of a polymer is produced. Is generated in a large amount, and when ejected from the die, there is a remarkable tendency to adhere to the die, the casting drum, or the film itself, and this has caused a stripe defect or an internal defect on the film surface.

Further, when the extruded polyester film is subsequently subjected to stretching, oligomers carried on the cast film are accumulated in the recesses of the stretching rolls during the subsequent longitudinal stretching, so that the surface of the running film is scratched. This has caused additional surface defects.

For this reason, in the conventional polyester film manufacturing process, it is necessary to frequently replace the base, clean the drum, and clean the rolls, which leads to a decrease in productivity. I was

Further, the conventional extruder for a polyester film uses the temperature of the molten resin to be extruded at its melting point (Tm).
Although a heating and cooling device is provided to control the temperature to less than + 40 ° C., the effect of preventing the generation of oligomers by this has not been sufficient.

In addition, since the extrusion step is a step of melting the resin, if the temperature of the molten resin is too low, there is a risk that unmelted material remains on the contrary. In the case of multi-product production ranging from a film to a thick film, since the required temperature of the molten resin varies depending on the product, the molding conditions for the production change and it is difficult to keep the quality constant.

On the other hand, as a method for preventing oligomer precipitation in the casting step, there is known a method of laminating a low oligomer resin on a polyester resin (Japanese Patent Application Laid-Open Nos. 63-197643 and 2-272713). However, this method further requires a composite extruder or a coating apparatus, so that the cost cannot be avoided, and there is a problem that the recoverability on the raw material side is deteriorated.

Further, in order to prevent defects due to oligomers at the time of film formation, a method of extracting and removing the oligomer on the surface of the unstretched film and then stretching the film has been proposed. Is significantly reduced.

Further, as a means for reducing the amount of oligomer contained, a method of subjecting a polyester resin chip as a raw material to solid phase polymerization is known, but this method avoids an increase in cost due to an increase in the number of solid phase polymerization steps. It is not yet practical because it cannot.

As described above, in the production process of a polyester film, particularly in the extrusion process, there is a strong demand for the improvement of productivity and film quality by suppressing the precipitation of oligomers, and various improvement methods have been studied. However, the improvement effect by them was still not enough.

[0015]

SUMMARY OF THE INVENTION The present invention has been achieved as a result of studying to solve the problems in the prior art described above.

Accordingly, an object of the present invention is to provide a high-quality polyester film which has a small amount of oligomer leaching on the film surface and has very few oligomer stains and surface defects during film formation, and an excellent productivity of this polyester film. It is to provide a manufacturing method based on the above.

[0017]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, by adding a special device to the extrusion process of the polyester film,
The inventors have found that a high-quality polyester film in which the amount of oligomers on the film surface is dramatically reduced than before can be obtained with excellent productivity, and reached the present invention.

That is, the present invention provides a polyester film obtained by a melt extrusion method, wherein the amount of extracted oligomer on the surface of the film is less than 2.0 mg / m ^2. It is.

Incidentally, the polyester film of the present invention comprises:
The content of the oligomer is not less than 0.6% by weight and less than 1.4% by weight, the ratio of the linear component contained in the extracted oligomer on the film surface is less than 30%, without laminating other films. Being composed of one layer, being a substantially non-oriented unstretched film, and a uniaxial or stretched film obtained by a melt extrusion method is stretched in one or both directions of the longitudinal direction and the width direction. It is a desirable condition to be a biaxially oriented film,
By satisfying these conditions, more excellent effects can be obtained.

The polyester film of the present invention having the above-mentioned properties is obtained by extruding a polyester resin heated and melted in an extruder from a flat die by a melt extrusion method.
In the method of forming a sheet, in the melting portion of the extruder,
After the polyester resin is once heated to a temperature equal to or higher than the melting end temperature (Tme) and lower than the thermal decomposition start temperature (Td), the surface temperature of the sheet-like molten resin at the exit of the flat die is changed to the melting end temperature (Tme). ), And cooled to a temperature equal to or lower than the temperature-falling crystallization start temperature (Tcb). The cooling of the sheet-like molten resin is performed by using a flat die, a filter, a gear pump,
It is desirable to do this in any of the polymer tubes above the stage.

Further, the polyester film of the present invention comprises:
An extruder having two or more stages is used. In the first stage of the extruder, the polyester resin is melted at its melting end temperature (T
me), after heating to a temperature lower than the thermal decomposition onset temperature (Td), in the second stage of the extruder, the temperature of the molten resin is lower than its melting end temperature (Tme), T
cb) It can also be produced by cooling to the above temperature and then extruding from a flat die into a sheet.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyester resin used in the present invention is:
A polymer having an ester group in the main chain obtained by condensation polymerization from a diol component and a carboxylic acid component. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, diphenic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, and sebacin. Acid, dimer acid, eicoic acid, dodecanedioic acid and the like are used, and as the diol component, ethylene glycol, trimethylene glycol, tetramethylene glycol, bisphenol and the like are used as typical examples.

Specific examples of the polyester resin include polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalate. However, these may be homopolymers, other diol components such as diethylene glycol, neopentyl glycol, polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6
A copolymer containing another dicarboxylic acid component such as naphthalenedicarboxylic acid as a copolymer component may be used.

In the present invention, PET and polyethylene-2,6-naphthalate are particularly preferably used from the viewpoints of mechanical strength, heat resistance, chemical resistance, durability and versatility of the obtained film. You.

The polyester resin used may contain various additives as long as the effects of the present invention are not impaired.
For example, an antioxidant, an antistatic agent, a crystallization agent, inorganic particles, and the like may be added.

In the melt extrusion method of the cast polyester film in the present invention, a polyester resin is supplied to a supply section using an extruder, and the resin is melted in a melting section by rotating a screw in a heated extruder. Next, the molten resin is guided to the base through the heated channel (polymer tube),
It is a method of extruding into a sheet on a cooled drum,
It is not particularly limited to this.

It is preferable that the polyester film extruded in the form of a sheet is then uniaxially or biaxially stretched by various stretching apparatuses depending on the purpose of improving mechanical strength and the like.

The thus obtained polyester film of the present invention has an extracted oligomer amount of 2.0 m on the film surface.
It is an important requirement that it is less than g / m ² from the viewpoint of preventing the oligomer from adhering to the drum or the stretching roll. Preferably it is less than 1.5 mg / m ² , more preferably 1.0 mg / m ² . That is, if the amount of the extracted oligomer on the film surface is less than 2.0 mg / m ² , there is little leaching of the oligomer on the film surface during film formation. In doing so, it is possible to make these devices less likely to be soiled. In addition, it is possible to suppress a flaw on the film surface generated at the time of stretching due to less contamination of the device such as a drum and a roll, and to obtain a film of higher quality. Further, in the next processing step, for example, it is possible to suppress the occurrence of defects such as uneven deposition and film omission during coating.

On the other hand, when the amount of the extracted oligomer on the surface of the film exceeds 2.0 mg / m ² , the oligomer stain may be conspicuous on the drum, the die and the roll several tens of minutes after the start of the film formation. And after several tens of hours,
It is not preferable because the drum, the base and the roll need to be replaced or cleaned.

In the film of the present invention, the content of the oligomer is preferably 0.6% by weight or more and less than 1.4% by weight from the viewpoint of raw material costs. More preferably, it is at least 0.8% by weight and less than 1.3% by weight. When the content of oligomer is less than 0.6% by weight, the amount of oligomer in the whole film is small and the amount of surface oligomer is also reduced. This is not preferred because the use of special equipment, the use of special polymers and additives, inevitably reduces productivity and increases costs.

On the other hand, when the content of the oligomer exceeds 1.4% by weight, the oligomer cannot be present in the film,
A large amount of precipitates and sublimates are deposited on the film surface and in the atmosphere, and even if the method of the present invention described below is used, it is not preferable because stains on the device and defects on the film surface cannot be sufficiently reduced.

In a polyester film having an oligomer content of 0.6% by weight or more and less than 1.4% by weight, the surface oligomer amount becomes 2.0 mg / m ² or more. In the film, the amount of the extracted oligomer is less than 2.0 mg / m ² by applying the production method described below, although the ordinary polyester chip obtained by the ordinary polymerization method and apparatus is used. Therefore, a favorable effect in terms of cost can be expected.

In the film of the present invention, the ratio of the linear component contained in the extracted oligomer on the film surface is less than 30%, which indicates that the oligomer adheres to a die, a casting drum, and a stretching roll. This is preferable because the effect of prevention can be enhanced and not only the quality of the film but also the productivity can be further improved. Further, from the viewpoint of further reducing the contamination of the apparatus, the ratio of the linear component contained in the extracted oligomer on the film surface is more preferably less than 25%, and further preferably less than 15%. In other words, particularly in the film forming process, oligomer dirt which is a problem in a die, a casting drum, a longitudinal stretching roll, etc. is mainly a linear oligomer which is easily evaporated and sublimated from a film, and is regarded as a problem more than a cyclic oligomer. I have. Therefore, by suppressing the linear oligomer component on the film surface, it becomes possible to significantly reduce such device contamination. When the ratio of the linear component contained in the extracted oligomer on the film surface becomes 30% or more,
Oligomer contamination on a die, a casting drum, and a longitudinal stretching roll is severe, and cleaning must be performed frequently, which is not preferable because productivity is deteriorated.

Here, the linear components in the extracted oligomer are terephthalic acid, terephthalic acid, except for cyclic bodies such as ethylene terephthalate cyclic trimer, ethylene terephthalate cyclic tetramer and ethylene terephthalate cyclic pentamer oligomer. It refers to a linear oligomer represented by monohydroxyethyl ester, terephthalic acid bishydroxyethyl ester, and the like, and the ratio is shown as a percentage with respect to the total amount of the oligomer extracted from the film surface. This linear component has a lower sublimation point than the cyclic component,
Many substances that easily evaporate, volatilize, and sublimate at the film forming temperature are included.

Further, the polyester film of the present invention comprises
It is preferable that a single layer, that is, a single layer is formed without laminating other films. As described above, in order to obtain a film having a small amount of extracted oligomer on the surface, a method of laminating a low-oligomer polymer film on the surface layer is generally employed. In this case, a composite extrusion device is used. There has been a problem that the cost is increased due to the necessity or conversion to a special polymer. However, the film of the present invention is advantageous because even if it is a single-layer extruded film having only one layer, the amount of extracted oligomer on the surface is small, so that the cost can be reduced both in terms of equipment and raw materials.

The polyester film of the present invention preferably has a characteristic that the amount of extracted oligomer on the surface is less than 2.0 mg / m ^{2 in} a substantially non-oriented unstretched film. That is, when secondary processing of an unstretched film, oligomer contamination in the secondary processing step can be suppressed, and even when subjected to stretching, since the amount of surface-extracted oligomer of the film before stretching is small, It is possible to suppress film-forming dirt in the stretching step and produce a uniaxially or biaxially oriented film with high productivity.

The monoaxially or biaxially oriented film thus obtained has high quality characteristics with less amount of oligomers extracted on the surface and scar defects due to oligomers.

To obtain the polyester film of the present invention having such properties, a sheet-like molten resin extruded from a flat die is prepared by treating a sheet-like molten resin having a surface temperature lower than a melting end temperature (Tme);
This is achieved by cooling to a temperature equal to or higher than the temperature drop crystallization start temperature (Tcb).

That is, the polyester film of the present invention is obtained by extruding a polyester resin heated and melted in an extruder from a flat die by a melt extrusion method into a sheet shape. After heating once to a temperature lower than the thermal decomposition onset temperature (Td), the surface temperature of the sheet-like molten resin at the exit of the flat die is lower than the melting end temperature (Tme) and higher than the temperature dropping crystallization start temperature (Tcb). It can be manufactured by cooling to a temperature.

According to the above-mentioned production method, the temperature distribution in the thickness direction of the sheet-like molten resin is high inside and low on the surface, so that migration of the oligomer to the surface due to thermal diffusion is suppressed. Also in the cast film obtained, it is possible to obtain a film in which the oligomer does not seep into the surface. In addition, among the oligomers, the effect is particularly large for linear components, and leaching of the linear oligomer onto the film surface can be drastically suppressed.

As the extruder used in the present invention, a usual one-stage type in which a supply part, a melting part, and a measuring part are provided in one apparatus, a supply and melting in the first stage, and a melting in the second stage. A two-stage type in which the functions of temperature equalization and measurement are divided into two stages is exemplified.

Since the extruder is a device for melting and quantitatively extruding the raw resin supplied in the form of chips,
If any one of the functions of supply, melting and metering is lacking, it is not preferable because the resin cannot be extruded stably.

Although the die in the present invention is not particularly limited, for example, Keiji Sawada, “Plastic extrusion molding and its application” (Seibundo Shinkosha Co., Ltd.)
, A manifold die (also referred to as a T die) having a cylindrical groove (manifold) inside,
It may be a fish tail die shaped like a fish tail, or a coat hanger die shaped in between.

The flat die is a part called a die hopper which usually spreads the molten resin in the width direction, and a final part which is formed after the molten resin is spread in the width direction and is formed into a desired shape, and has a certain slit gap. And a portion called a land portion which is a parallel portion. The molten resin is released to the atmosphere immediately after passing through the land, and is extruded on a casting drum.

The heating temperature of the polyester resin in the melting section in the extruder is determined by the melting end temperature (T
me) to ensure that no unmelted material remains. The melting point of the resin can be easily measured by a differential scanning calorimeter (DSC). Generally, in the case of a polymer material, the melting point is not observed as a single point, but as a broadened peak. Here, it is necessary to adopt not the melting peak temperature (Tm) but the temperature at the end of the tail (melting end temperature, Tme) as the melting point that determines the heating temperature in the extruder. That is, the melting peak temperature (T
In m), most of the resin is melted, but it is not preferable because the resin at the end of the foot may not be melted and may remain in an unmelted state.

The heating temperature of the polyester resin is preferably lower than the thermal decomposition onset temperature (Td) of the polyester resin. Is not preferred. Thermal decomposition onset temperature (Td) of polyester resin
Can be simply measured by a thermogravimetric device (TG). That is, when the sample is heated from room temperature in a nitrogen atmosphere, the TG curve shows a constant value with the initial weight until pyrolysis, but when gas is generated by pyrolysis, the sample weight decreases. Begins to decrease. And in the present invention,
The temperature at the critical point where the TG curve begins to decrease was adopted as the thermal decomposition onset temperature (Td).

In the present invention, the surface temperature of the sheet-like molten resin at the exit of the flat die is determined by the melting end temperature (Tme).
It is an important requirement that the cooling be performed so that the temperature is lower than or equal to or lower than the temperature drop crystallization start temperature (Tcb).

That is, the present inventors set the surface temperature of the sheet-like molten resin to be lower than the internal temperature of the molten resin at the exit of the flat die, so that the movement due to the thermal diffusion of the oligomer moves from the surface to the internal direction. And found that the distribution of oligomers was small on the surface and increased inside. Therefore, the total amount of oligomers does not change in the whole film, but the oligomers are trapped inside the molten resin, which reduces the amount of oligomers leaching on the surface and suppresses the generation of dirt and scratches by the surface oligomers It is possible to do.

The cooling of the molten resin is preferably carried out in a flat die from the viewpoint of the simplicity of the apparatus, but is preferably carried out in the steps after the filter from the viewpoint of the cooling capacity. More preferably, cooling is performed in the process after the polymer tube, and more preferably in all processes after the extruder.

When the above-mentioned two-stage type extruder is used, the first stage is heated to a temperature not lower than the melting end temperature (Tme) of the polyester resin and lower than the thermal decomposition starting temperature (Td). Then, in the second stage, the molten resin is cooled to a temperature lower than the melting end temperature (Tme) and higher than the temperature-fall crystallization start temperature (Tcb), and then extruded from a flat die into a sheet to form a melt. The resin can also be cooled. The effect of this cooling is higher as the cooling temperature is lower. If desired cooling is not performed at the exit of the flat die, the oligomer in the molten resin exudes to the film surface at the time of extrusion, which is not preferable because it causes drum and roll contamination.

The cooling device used in the present invention is not particularly limited. For example, various devices can be used in any of an extruder, a polymer tube, a gear pump, a filter, and a die. For cooling, it is possible to control the temperature by setting the conventional equipment such as heat insulator and electric heater, but it is also necessary to provide a cooling hole near the flow path of the molten resin and let the refrigerant flow through it Is particularly recommended in terms of cooling efficiency. As the refrigerant in this case, air or water is preferably used. In addition, by inserting a thermocouple penetrating the flow channel into each device, it becomes possible to measure the resin temperature.

It is important to cool the sheet-like molten resin to a temperature lower than the melting end temperature (Tme) of the polyester resin and higher than the temperature-falling crystallization start temperature (Tcb). During this cooling, the temperature of the molten resin that is in contact with the liquid contact surface of the apparatus is substantially the same as the liquid contact surface. In the case of a polymer resin, even if the resin in a molten state is cooled below its melting end temperature (Tme), it does not solidify in a short time and can maintain a so-called supercooled liquid phase state. When the temperature becomes lower than the temperature (Tcb), the resin starts to crystallize,
The surface of the extruded film is unfavorably undesirably extruded due to surface roughness, extrusion abnormalities, uneven flow, etc., and solidification over time, which makes it impossible to extrude with a normal extruder.

In the present invention, the molten resin is cooled by cooling the liquid contact surface, and what is important at that time is that the molten resin is never solidified. It is important to use a supercooled state of a polymer and extrude it in a liquid phase even if it is at or below the melting point. In addition, when performing heat retention or heating at the mouthpiece from the measuring section of the extruder, the set temperature is set to a temperature equal to or lower than the thermal decomposition start temperature (Td) of the polyester resin so that the molten resin does not undergo thermal decomposition or thermal degradation. It is desirable to keep.

Thus, according to the present invention, it is possible to produce a polyester film having very few stains on a die, a drum, and a roll, and a film surface defect with excellent productivity. The quality is greatly improved.

[0056]

[Evaluation and measurement methods of physical properties]

(1) Amount of extracted oligomer on the film surface Fifteen square test pieces of 4.5 cm x 4.5 cm are cut out from the sample film. Next, a beaker containing 20 ml of ethanol for extraction is put into an ultrasonic cleaner containing water, and the test pieces are subjected to ultrasonic treatment one by one for 2 minutes. After washing all 15 test pieces, the extract was made up to 30 ml with ethanol, and the resulting extract 1
Evaporated 0 ml is redissolved in 2 ml of methanol, filtered, and quantitatively analyzed by high performance liquid chromatography (HPLC). The quantitative analysis was performed on the following cyclic or linear oligomers present in the sample.

• PET cyclic oligomer (tri- to pentamer) • dimethyl terephthalate (DMT) • hydroxyethyl methyl terephthalate (MH)
T) ・ Terphthalic acid bishydroxyethyl ester (BH
T)-Terephthalic acid (TPA)-Terephthalic acid monomethyl ester (MMT)-Terephthalic acid monohydroxyethyl ester (HH
T) Quantitative analysis was performed under the following two conditions according to the type of oligomer to be analyzed.

Cyclic oligomer, DMT, MHT, BHT analysis conditions HPLC analyzer: Pump (LC-6A) manufactured by Shimadzu Corporation: System controller (SCL-6A) manufactured by Shimadzu Corporation: Shimadzu Corporation UV detector (SPD-6AV) Column: INERSIL ODS-2 4.6 × 250 mm, developed by Gaschrom Industry Co., Ltd. Developing solvent: A = pure water, B = acetonitrile Flow rate: 1.5 ml / min Wavelength: 242 nm Column temperature: 45 ° C

Analysis conditions for TPA, MMT, HHT HPLC analyzer: Pump (100A) manufactured by Beckmann-Altex: Controller (420) manufactured by Beckmann-Altex: Ultraviolet detector (SPD-6AV) manufactured by Shimadzu Corporation : INERTSIL ODS-2 4.6 × 150 mm, manufactured by Gaschrom Industry Co., Ltd. Developing solvent: A = PIC-A, B = Methanol Flow rate: 0.8 lm / min Wavelength: 242 nm Column temperature: 45 ° C.

For quantification, a calibration curve was prepared using a sample of each oligomer whose concentration was known in advance, and quantification was performed from the peak area of the HPLC chromatogram. From the obtained amount of oligomer, the amount of oligomer in the whole extract was calculated, divided by the total area of the extracted film, and converted into the amount of oligomer per unit area.

(2) Content of Oligomer in Film 100 mg of the polymer was dissolved in 5 ml of orthochlorophenol and subjected to liquid chromatography (Varian).
Model 8500), and the ratio to the polymer (% by weight) is shown.

(3) Ratio of linear components contained in the extracted oligomer on the film surface From the result of the measurement of the amount of the extracted oligomer on the film surface described above, the total amount of all the obtained oligomers was calculated as Wt (mg / mg /
m ² ), the sum of PET cyclic oligomers (tri- to pentamers)
As c (mg / m ² ), the ratio of the linear component was represented by percentage (%) according to the following equation.

Ratio of linear component (%) = [(Wt−Wc)
/ Wt] × 100

(4) Thermal Characteristics A “robot” DSC RDC220 manufactured by Seiko Electronics Industries, Ltd. was used as a differential scanning calorimeter, and a disk station SSC / 520 manufactured by the company was used as a data analyzer.
Using 0, about 5 mg of the sample was heated from room temperature to 400 ° C. at a rate of 20 ° C./min on an aluminum saucer. The starting temperature of the melting peak observed at this time is T
mb, the peak temperature was the melting point (Tm), and the peak end temperature was the melting end temperature (Tme). Also, about 5m sample
g was heated from room temperature to (Tm + 40 ° C.) at a rate of temperature rise of 20 ° C./min, melted and held for 5 minutes, and cooled at a rate of temperature drop of 20 ° C./min. At this time, the start temperature of the cooling crystallization peak observed is Tcb, the peak temperature is Tc, and the end temperature of the peak is Tcb.
ce.

(5) Thermal decomposition temperature The thermogravimetric measurement was carried out by using a thermogravimetric analyzer (TGA-50H) manufactured by Shimadzu Corporation and an analyzer Thermal Analyzer (TA-50), and personal data processing. Performed in combination with a computer. Using a polyester resin vacuum-dried at 110 ° C all day and night, about 15
mg was weighed and set in the furnace. The furnace was placed under a nitrogen atmosphere and heated from room temperature to 600 ° C. at a rate of 5 ° C./min.
Hold for 60 minutes. From the TG curve after the analysis, the temperature at the critical point at which the weight of the sample began to decrease was read and defined as the thermal decomposition onset temperature (Td).

(6) Temperature of Liquid Contact Surface The temperature of the liquid contact surface of the apparatus in each step is determined by forming a hole in the apparatus base material near the outlet of the molten resin flow path in each step up to a position 2 mm short of penetrating the flow path. The measurement was performed by inserting a thermocouple into this.

(7) Internal Temperature of Polymer The internal temperature of the molten resin extruded from the exit of the flat die was measured by inserting a thermocouple into the slit of the die.

(8) Surface Temperature of Polymer The surface temperature of the sheet-like molten resin extruded from the exit of the flat die is measured by a radiation thermometer THI- manufactured by Tasco Japan Co., Ltd.
The emissivity ε was measured at 0.95 using 300.

(9) Oligomer dirt on the die, casting drum and stretching roll Before the start of film formation, the die, casting drum and stretching roll are thoroughly cleaned, and the dirt condition 10 hours after the start of the film formation is checked. Observed by visual inspection, if there is almost no dirt at first glance, ○ indicates that the dirt is very thin, but the dirt can be confirmed but there is no problem with continued use. Were evaluated as "x".

(10) Defects on the surface of the film The film was actually formed, the cast film and the uniaxially stretched film after the longitudinal stretching were collected, the surroundings were darkened, the film was illuminated with a plurality of lights, and the film was transmitted with the transmitted light. Observe. At this time, in the case of cast film, 5m length,
In the case of a uniaxially stretched film, the surface of a film having a length of 20 m was observed, and the number of surface defects that could be visually confirmed was counted. When the number of surface defects 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. The case where there was almost no defect and the surface property was good was evaluated as “○”, and the case where no defect was observed was evaluated as “◎”.

[0071]

EXAMPLES The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Examples 1-4 PET having an intrinsic viscosity of 0.65 was used as a polyester resin. The thermal characteristics of this PET were measured using a DSC. Tmb: 240 ° C., Tm: 255 ° C.,
me: 268 ° C, Tcb: 203 ° C, Tc: 188 ° C, Tc
e: 138 ° C. From the thermogravimetric measurement, the thermal decomposition onset temperature Td was 302 ° C.

The PET pellets are vacuum-dried at 180 ° C. for 3 hours, supplied to the hopper of the extruder, fed from the supply section to the melting section, compressed and melted at 280 ° C., and then sent to the measuring section. It is. At this time, the discharge amount of the molten polymer was fixed at 150 kg / hr.

Thereafter, the molten resin is supplied from the polymer tube to the gear pump, and is sent to the molding flat die through the polymer tube and the filter.

The measuring section of the extruder, each polymer tube,
The gear pump, the filter, and the flat die are provided with cooling holes in the vicinity of the molten resin flow path, and have a structure capable of cooling by flowing cooling water or cooling air through the cooling holes. Heating is also possible with an electric heater.

Next, the sheet-like molten resin extruded from the flat die is subjected to static electricity while applying a surface temperature of 25 ° C.
A cast film was obtained by cooling and solidifying on a casting drum kept at a constant temperature.

The obtained cast film was guided to a stretching roll and stretched 3.0 times in the machine direction at 95 ° C. to obtain a uniaxially stretched film.

In the above, the apparatus was thoroughly cleaned before the start of film formation, and stains on the die, the casting drum, and the stretching roll were observed 20 hours after the start of film formation.

At this time, the set temperature of the liquid contact surface in each step, the polymer internal temperature at the center of the flat die outlet,
The surface temperature is shown in Table 1, and the results of observation of oligomer stains on a die, a casting drum, and a stretching roll, the amount of oligomer contained in the obtained cast film and uniaxially stretched film,
Table 2 shows the results of the evaluation of the amount of the surface-extracted oligomer, the ratio of the linear component, and the surface defect.

As is clear from the results shown in Tables 1 and 2, in Example 1 in which the molten resin was cooled only in the flat die, the polymer internal temperature at the flat die outlet was 284 ° C. The surface temperature was as low as 245 ° C. Although the oligomer content of the obtained cast film was 1.2% by weight, the amount of oligomers extracted on the surface was 1.8 mg / m ² and the ratio of linear components was very small at 25%. Almost no oligomer stains on the stretching roll were observed. No surface flaws caused by the oligomer were found on the obtained cast film. Further, even though the uniaxially stretched film had some drawbacks, it was of no problem to use.

In Example 2 in which the molten resin was cooled with the filter and the die, the internal temperature of the polymer at the exit of the flat die was 283 ° C., whereas the surface temperature was lowered to 242 ° C. , The amount of surface-extracted oligomers and the linear components were further reduced. Almost no oligomer stains were found on the die, the casting drum and the stretching roll. Also, no surface flaws caused by the oligomer were found on the obtained cast film. Further, even though the uniaxially stretched film had some drawbacks, it was of no problem to use.

In Example 3 in which the cooling of the molten resin was performed after the gear pump, the internal temperature of the polymer at the outlet of the flat die was as high as 281 ° C., whereas the surface temperature was 23 ° C.
The temperature was lowered to 9 ° C., and the temperature difference between the inside and the surface became even larger. The surface cast oligomer amount of the obtained cast film was 1.0 mg / m ² , the linear component was further reduced to 18%, and almost no oligomer contamination on the die, the casting drum, and the stretching roll was observed. Also, no surface flaws caused by the oligomer were found on the obtained cast film. Furthermore, even in the uniaxially stretched film, no surface flaw was recognized, and a high quality film was obtained.

Further, in Example 4 in which the molten resin was cooled in all steps from the measuring section of the extruder to the die, the internal temperature of the polymer at the flat die outlet was 279 ° C.
However, the surface temperature was further lowered to 236 ° C., and the amount of surface-extracted oligomers and linear components of the obtained cast film were further reduced. Almost no oligomer contamination on the die, casting drum and stretching roll was observed, and no surface flaws caused by the oligomer were found on the obtained cast film and uniaxially stretched film.

Comparative Examples 1 to 4 Films were formed using the same apparatus and the same PET resin as in Examples 1 to 4. Further, the discharge amount of the polymer, the casting conditions and the uniaxial stretching conditions were the same as in Examples 1 to 4. Table 1 shows the set temperature of the liquid contact surface, the internal temperature of the polymer at the center of the flat die outlet, and the surface temperature in each step.
Each was changed as shown in.

In each case, the results of observing oligomer stains on the die, the casting drum, and the stretching roll,
Table 2 also shows the evaluation results of the content of the oligomer, the amount of the surface-extracted oligomer, the ratio of the linear component, and the surface defect of the obtained cast film and the uniaxially stretched film.

As is clear from the results shown in Tables 1 and 2, in all the processes from the extruder measuring section to the flat die, cooling was not performed, and in Comparative Example 1 in which the liquid contact surface temperature was 280 ° C., the flattening was performed. The polymer internal temperature and surface temperature at the center of the die exit were almost the same at 285 ° C. and 283 ° C., respectively. As a result, although the amount of oligomer contained in the obtained cast film was almost the same as in Example 1, the amount of oligomer extracted on the surface was 6.2 mg.
/ M ² . In addition, the linear component in the extracted oligomer was contained as much as 42%. A large amount of powdery oligomer was present on the lower surface of the lip of the mouthpiece, and it was observed that a white oligomer was attached to the casting drum or the stretching roll so that the background became invisible. Further, in the obtained uniaxially stretched film, a lot of scratches and foreign matters which are considered to be oligomer defects were observed.

In Comparative Example 2 in which the temperature of only the measuring section of the extruder was lowered, the polymer surface temperature at the exit of the flat die was hardly lowered to 279 ° C., and the amount of the surface-extracted oligomer was 5.4 mg / kg. m ² , the ratio of linear components is also 3
9% did not decrease much. Many dirt caused by the oligomer was observed on the apparatus, and the surface of the obtained film was more flawed than in Example 1, and was particularly remarkable in the case of a uniaxially stretched film.

In Comparative Example 3 in which only the measuring section of the extruder and the temperature of the polymer tube were lowered, the polymer surface temperature at the exit of the flat die was slightly lowered to 275 ° C. 5.0 mg / m ² ,
The linear component was not so reduced to 38%. Many stains caused by the oligomer were also found on the apparatus, and both the cast film and the uniaxially stretched film obtained had surface scratch defects caused by the oligomer.

Further, in the flat die, cooling was performed to 200 ° C. lower than Tcb, and in the other steps, in the comparative example 4 in which the set temperature was set to 280 ° C., the cooling was started, and then the cooling was started.
After about minutes, the polymer at the tip of the flat die starts to crystallize white, and after 25 minutes, the discharge from the flat die stops completely and the filtration pressure of the extruder sharply increases,
It became impossible to extrude.

[0090]

[Table 1]

[Table 2]

[0091]

As described above, according to the present invention,
It is possible to produce polyester films with extremely low productivity due to die and casting drums caused by oligomers, as well as very few draw roll stains and film surface defects, and the resulting polyester films are caused by oligomers. There are few scratches and defects, and the quality is greatly improved.

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Claims (12)

[Claims] 1. A polyester film obtained by a melt extrusion method, wherein the amount of extracted oligomer on the surface of the film is less than 2.0 mg / m ² . 2. The composition according to claim 1, wherein the content of the oligomer is 0.6% by weight or more.
The polyester film according to claim 1, which is less than 1.4% by weight. 3. The polyester film according to claim 1, wherein a linear component contained in the extracted oligomer on the film surface is less than 30%. 4. The method according to claim 1, wherein the film is formed of one layer without laminating another film.
The polyester film according to any one of the above. 5. The polyester film according to claim 1, which is a substantially non-oriented unstretched film. 6. A film obtained by a melt extrusion method,
The polyester film according to any one of claims 1 to 4, wherein the polyester film is a uniaxially or biaxially oriented film stretched in one or both directions of a longitudinal direction and a width direction. 7. A method of extruding a polyester resin heated and melted in an extruder from a flat die into a sheet by a melt extrusion method, wherein the polyester resin is melted at a melting point in the extruder at a melting end temperature (Tme). that's all,
After once heating to a temperature lower than the thermal decomposition start temperature (Td), the surface temperature of the sheet-like molten resin at the flat die outlet is lower than the melting end temperature (Tme) and equal to or higher than the temperature drop crystallization start temperature (Tcb). The method for producing a polyester film according to any one of claims 1 to 6, wherein cooling is performed so that 8. The method for producing a polyester film according to claim 7, wherein the cooling of the sheet-like molten resin is performed in a flat die. 9. The cooling of the sheet-like molten resin is performed in a filter.
3. The method for producing a polyester film according to item 1. 10. The method for producing a polyester film according to claim 7, wherein the cooling of the sheet-like molten resin is performed by a gear pump. 11. The method for producing a polyester film according to claim 7, wherein the cooling of the sheet-like molten resin is performed in one or more stages of polymer tubes. 12. An extruder having two or more stages is used. In the first stage of the extruder, the polyester resin is melted at a temperature equal to or higher than its melting end temperature (Tme) and at a thermal decomposition starting temperature (Td).
After being heated to a temperature of less than 2 ° C., the molten resin is cooled in the second stage of the extruder so that the temperature of the molten resin is lower than the melting end temperature (Tme) and higher than the temperature-fall crystallization start temperature (Tcb). The method for producing a polyester film according to any one of claims 1 to 6, further comprising extruding a sheet from a flat die.