JP2015098548A - Method for producing polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film which suppresses the melt pressure low in producing the polyester film, can reduce the replacement frequency of a filter, has a small cyclic trimer content in the film and can be suitably used for a touch panel.SOLUTION: There is provided a method for producing a polyester film in which a polyester layer is formed by melt-extruding a polyester resin containing 60 wt.% or more of a polyester (A) having a terminal carboxyl group amount (AV) of 20 equivalent/t or less and an intrinsic viscosity of 0.65 dl/g or less.

Description

  The present invention relates to a method for producing a polyester film having a specific polyester layer and suitable for a touch panel.

  Conventionally, in touch panel applications, various methods such as a resistive film method and a capacitance method are employed depending on the position detection method. Among them, the popularization of the resistive film type tends to increase by taking advantage of its simple structure and excellent cost performance. The structure of the touch panel using the resistance film method is generally such that a transparent conductive laminate and a glass with a transparent conductive thin film are arranged to face each other via a spacer, and an electric current is passed through the transparent conductive laminate to be transparent. It consists of a structure that measures the voltage in glass with a conductive thin film. Utilizing the principle that when a transparent conductive laminate is brought into contact with a glass with a transparent conductive thin film through a pressing operation with a finger or a pen, the contact portion is energized to detect the position of the contact portion. ing. Moreover, as an example of adopting the resistance film method, an automatic teller machine, a display board of a train ticket machine, and the like are exemplified.

  In the present invention, the transparent conductive laminate is a laminate having a transparent conductive thin film, and the transparent conductive thin film is formed on a film substrate. A transparent conductive laminate is generally provided with a hard coat layer so as to improve transparency and withstand a pressing operation for a touch panel, which contributes to improvement of scratch resistance and the like. ing.

  In the manufacturing process of the transparent conductive laminate, it is generally heat-processed. For example, in order to form a transparent conductive film, an ITO film is formed by a sputtering method, and then heat treatment is performed at 150 ° C. for crystallization (Patent Document 1), or in the production of a conductive laminated film. When it is allowed to stand at 150 ° C. for 1 hour for low heat shrinkage treatment (Patent Document 2), or when processing a transparent conductive film, heat treatment at about 150 ° C. may be required to print a silver paste or the like. Yes (Patent Document 3). In the transparent conductive thin film manufacturing process, with heat treatment in a high temperature atmosphere, low molecular weight substances (especially cyclic trimers) contained in the polyester film precipitate and crystallize on the film surface, resulting in coating defects and the like. In some cases, it is difficult to obtain a highly accurate transparent conductive thin film.

  As a measure for preventing the above-described cyclic trimer precipitation, for example, it has been proposed to provide a curable resin layer made of a crosslinked product of a silicone resin and an isocyanate resin on a polyester film (Patent Document 3). However, the curable resin layer is formed by thermosetting, needs high-temperature treatment for dissociation of the blocking agent of the isocyanate resin, and is in a situation where curling and sagging are likely to occur during processing, Care must be taken in handling.

  As a measure for preventing cyclic trimer precipitation of a polyester film other than providing a curable resin layer, it has been proposed to use a polyester resin having a high intrinsic viscosity as a raw material for forming a polyester film (Patent Document 4). However, polyester with a high intrinsic viscosity has a high melt pressure in the melt extrusion process, so the resin temperature at the time of melting rises, polyester heat deterioration products are likely to occur, and the occurrence of blisters is high, resulting in the frequency of filter replacement. This causes a problem of high.

JP 2007-200823 A JP 2007-42473 A JP 2007-320144 A JP-A-8-283545

  The present invention has been made in view of the above circumstances, and the problem to be solved is that the melt pressure can be kept low during the production of the polyester film, the filter replacement frequency can be lowered, and the cyclic trimer in the film. An object of the present invention is to provide a polyester film that has a low body weight and can be suitably used for a touch panel.

  As a result of intensive studies in view of the above circumstances, the present inventor has found that the above-mentioned problems can be solved by using a polyester having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is a polyester containing 60% by weight or more of a polyester (A) having a terminal carboxyl group amount (AV) of 20 equivalent / t or less and an intrinsic viscosity (IV) of 0.65 dl / g or less. The present invention resides in a method for producing a polyester film, wherein the polyester layer is formed by melt-extruding a resin.

  According to the present invention, a polyester film suitable for a touch panel can be provided, and the industrial value of the present invention is high.

  The polyester layer referred to in the present invention is a layer constituting a stretched film, if necessary, after cooling a molten polyester sheet extruded by a so-called extrusion method that is melt-extruded from an extrusion die. In the case of a single layer film, the polyester layer represents the entire polyester film. In the case of a polyester film having two or more layers, each layer is defined as a polyester layer.

  In the present invention, the polyester used for the polyester film refers to a polyester obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. Among these, polyethylene terephthalate (PET) is preferable.

  The amount of the compound in the polyester (A) used in the present invention is determined by an analysis method using a fluorescent X-ray analyzer described later. For example, the content of each of titanium element, phosphorus element, antimony element and manganese element is Detected.

  The titanium element content in the polyester (A) of the present invention is preferably 20 ppm or less, more preferably 15 ppm or less, and particularly preferably 9 ppm or less. Although there is no particular lower limit, in practice, about 2 ppm is the lower limit in the current technology. If the content of the titanium compound is too high, a cyclic trimer is formed as a by-product in the process of melt-extruding the polyester, and is precipitated and crystallized on the surface of the film. When the titanium element is not contained at all, the productivity of the polyester raw material is inferior, and the polyester raw material reaching the target degree of polymerization may not be obtained.

  The phosphorus element in the polyester (A) used in the present invention is usually derived from a phosphoric acid compound and is added during the production of the polyester. In the present invention, the amount of phosphorus element in the polyester component is preferably in the range of 30 ppm or less, more preferably in the range of 20 ppm or less, and particularly preferably in the range of 15 ppm or less. Although there is no particular lower limit, in practice, about 3 ppm is the lower limit in the current technology. If the amount of phosphorus element is too large, depolymerization of the polyester resin is likely to occur, and the amount of cyclic trimer tends to increase. When there is too little phosphorus element amount, the polymerization activity of polyester (A) will become low, and there exists a tendency for a production rate to fall.

  Examples of the phosphoric acid compound to be used include known ones such as phosphoric acid, phosphorous acid or its ester phosphonic acid compound, phosphinic acid compound, phosphonous acid compound, and phosphinic acid compound. Acid, dimethyl phosphate, trimethyl phosphate, diethyl phosphate, triethyl phosphate, dipropyl phosphate, tripropyl phosphate, dibutyl phosphate, tributyl phosphate, diamyl phosphate, triamyl phosphate, dihexyl phosphate, Examples include trihexyl phosphate, diphenyl phosphate, triphenyl phosphate, and ethyl acid phosphate.

  The intrinsic viscosity (IV) of the polyester (A) used in the present invention is 0.65 dl / g or less, preferably 0.64 dl / g or less. When the intrinsic viscosity (IV) of the polyester (A) is 0.65 dl / g or less, the melt pressure in the melt-extrusion process can be lowered, so that the resin temperature at the time of melting is reduced, and a polyester thermal degradation product is generated. This makes it difficult to generate fuzz, and as a result, the frequency of filter replacement can be kept low. The lower limit of the intrinsic viscosity (IV) of the polyester (A) of the present invention is not particularly set, but 0.50 dl / g is realistic from the viewpoint of preventing breakage during film forming.

  The terminal carboxyl group amount (AV) of the polyester (A) used in the present invention is 20 equivalents / t or less, preferably 14 equivalents / t or less, more preferably 11 equivalents / t or less. When the terminal carboxyl group amount (AV) of the polyester (A) is 20 equivalent / t or less, a polyester film having a small number of cyclic trimers can be obtained. On the other hand, although there is no lower limit of the terminal carboxyl group amount AV of the polyester (A), it is about 5 equivalent / t from the viewpoint of the efficiency of the polycondensation reaction and the decomposition in the melt extrusion process.

  It is desirable that the polyester layer in the present invention contains fine particles in order to improve workability in a film winding process, a coating process, a vapor deposition process, and the like. The fine particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, lithium phosphate, magnesium phosphate, calcium phosphate, lithium fluoride, aluminum oxide, and kaolin, and organic particles such as acrylic resin and guanamine resin. In addition, there can be mentioned, but not limited to, precipitated particles in which the catalyst residual is made into particles. Among these particles, porous silica particles that are aggregate particles of temporary particles are particularly preferable. Since the porous silica particles are less likely to generate voids around the film when the film is stretched, the porous silica particles have the feature of improving the transparency of the film.

  The average particle size of the primary particles constituting the porous silica particles is preferably in the range of 0.001 to 0.1 μm. If the average particle size of the primary particles is less than 0.001 μm, ultrafine particles are generated by crushing at the slurry stage, which may form aggregates and cause haze to increase. On the other hand, when the average particle size of the primary particles exceeds 0.1 μm, the porosity of the particles is lost, and as a result, the feature of generating less voids may be lost.

  Furthermore, the pore volume of the aggregated particles is usually 0.5 to 2.0 ml / g, preferably 0.6) to 1.8 ml / g. When the pore volume is less than 0.5 ml / g, the porosity of the particles is lost, voids are easily generated, and the transparency of the film tends to be lowered. When the pore volume is larger than 2.0 ml / g, crushing and aggregation are likely to occur, and it may be difficult to adjust the particle size.

  The method for adding particles during the production of the polyester layer in the present invention is not particularly limited, and a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction. The condensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a bent type kneading extruder and a polyester raw material, or a blend of dried particles and a polyester raw material using a kneading extruder. It is done by the method to do.

  In addition, it is preferable not to contain as much as possible a metal compound that can act as a catalyst in order to suppress thermal decomposition and hydrolysis, but in order to reduce the volume resistivity at the time of melting in order to improve the productivity of the film, magnesium, Metals such as calcium and lithium can be usually contained in the polyester component if they are 300 ppm or less, preferably 250 ppm or less.

  In addition, as a polycondensation catalyst of polyester (A), an antimony compound can be used, and antimony trioxide is particularly preferable. As a co-catalyst when using antimony trioxide, a manganese compound is preferable, and manganese acetate tetrahydrate is particularly preferable. The amount of the antimony compound and the amount of the manganese compound in the polyester (A) is preferably 400 ppm or less, more preferably 300 ppm or less, and particularly preferably 200 ppm or less as the element amount.

  In order to reduce the amount of the cyclic trimer in the polyester (A), it is preferable to perform solid phase polymerization. However, when the intrinsic viscosity of the polyester (A) is high, there is a problem that the pressure tends to be high during the production of the polyester film. Therefore, when solid-phase polymerization is performed, a polyester chip having a reduced amount of cyclic trimer is produced by holding the melt-polymerized polyester chip for a long time at a high temperature, and then the degree of vacuum is increased to adjust to a predetermined intrinsic viscosity. It is preferable to adopt a technique.

  In addition to the above-mentioned particles, conventionally known antioxidants, heat stabilizers, lubricants, antistatic agents, and dyes can be added to the polyester layer obtained by the production method of the present invention as necessary. . Further, for the purpose of improving the weather resistance, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber or the like can be contained in the range of 0.01 to 5.0 parts by weight with respect to the polyester component.

  The thickness of the polyester film containing the polyester layer obtained by the production method of the present invention is not particularly limited as long as it can be formed as a film, but is usually 1 to 500 μm, preferably 15 to 400 μm, Preferably it is the range of 20-300 micrometers.

  The ratio of the polyester (A) mixed by the production method of the present invention is 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and most preferably 85% by weight or more. When the content of the polyester (A) is less than the above, the amount of the cyclic trimer in the outermost layer of the polyester film obtained by the production method of the present invention is undesirably increased.

  The polyester film containing the polyester layer obtained by the production method of the present invention can be made into a single-layer film composed of one layer using one melt extruder.

  The polyester film containing the polyester layer obtained by the production method of the present invention can be formed into a laminated film of two layers or three layers or more by a so-called coextrusion method using two or three or more melt extruders. As a layer structure, an X / Y structure using an X raw material and a Y raw material, or an X / Y / X structure, and further a film having an X / Y / Z structure or other structure using a Z raw material. Can do.

  If it is the structure of X / Y, it is desirable that polyester (A) is contained in either X or Y layer. In the X / Y / X configuration, it is desirable that X contains polyester (A). In the X / Y / Z configuration, it is desirable that polyester (A) is contained in either one of the X or Z layers.

  Hereinafter, although the manufacturing method of the polyester layer of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.

That is, a dried or undried polyester chip (polyester component) by a known method is supplied to a kneading extruder, heated to a temperature equal to or higher than the melting point of the polyester component, and melted. Next, the melted polyester is extruded from a die, and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed. In the melt extrusion process, the cyclic trimer increases depending on the conditions. Therefore, in the present invention, the residence time of the polyester in the extruder in the extrusion process is shortened. Dry sufficiently so that the amount is usually 50 ppm or less, preferably 30 ppm or less. When a twin screw extruder is used, a vent port is provided, usually 40 hectopascals, preferably 30 hectopascals, more preferably 20 hectopascals or less. A method such as maintaining the reduced pressure is adopted.
The extruder using the polyester (A) is preferably a vent type twin screw extruder from the viewpoint of preventing an increase in the amount of the cyclic trimer.

  It can be said that the deaeration efficiency of the vent type twin-screw extruder is better when the screw rotation speed is higher for a certain extrusion amount. That is, when the screw rotation speed is increased with respect to a certain extrusion amount, the surface of the polyester existing on the screw surface can be forcibly renewed, and the degassing efficiency from the molten polyester increases accordingly. . As a result, the retention of the intrinsic viscosity of the polyester is improved. That is, an increase in the amount of cyclic trimer accompanying polyester molecular decomposition is suppressed.

  When the internal diameter (diameter) of the cylinder of the vent type twin screw extruder is D (mm), the extrusion amount Q (kg / hr) per unit time and the screw rotation speed N (rpm) are expressed by the following formula (I ), Preferably melt extrusion under conditions satisfying the following formula (II), more preferably the following formula (III). By satisfying such conditions, it is possible to increase the deaeration efficiency while suppressing excessive heat generation due to the shearing action of the screw, and to prevent an increase in the amount of the cyclic trimer of the polyester.

次の（IV）式に示す条件では、回転数が押出量に対して高すぎるため、スクリューの剪断による発熱が過多となり環状三量体量が増大する傾向がある。また、次の（Ｖ）式に示す条件では、回転数が押出量に対して低すぎるため、減圧下での溶融樹脂表面の更新度が低下して十分な脱気が行えずに環状三量体量が増大する傾向がある。

Under the conditions shown in the following formula (IV), since the rotational speed is too high with respect to the extrusion amount, heat generation due to the shearing of the screw becomes excessive, and the amount of the cyclic trimer tends to increase. In addition, under the conditions shown in the following formula (V), the rotational speed is too low with respect to the extrusion amount, so that the degree of renewal of the molten resin surface under reduced pressure is reduced and sufficient deaeration cannot be performed. There is a tendency for body weight to increase.

  When a substantially undried polyester is used, the moisture inside the polyester is degassed by a pressure reducing action from the vent hole. In order to increase the deaeration efficiency of moisture, the degree of vacuum of the vent hole is usually 40 mmHg or less, preferably 30 mmHg or less, more preferably 10 mmHg or less.

  In the present invention, when the polyester sheet is melt-extruded on the surface of the casting drum, an electrostatic contact method, an air knife method, a nip roll method of niping with two rolls, etc. are appropriately employed in order to improve the adhesion of the polyester sheet to the casting drum. be able to.

  In the present invention, the sheet thus obtained is stretched in the biaxial direction to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times in the longitudinal direction at 70 to 145 ° C. to form a longitudinally uniaxially stretched film, and then in the transverse direction at 90 to 160 ° C. Stretch 2-6 times and move to heat setting step.

  When a vented twin screw extruder is used, as described above, either substantially dry or undried polyester resin can be used, but even if substantially undried polyester is used, The increase in trimer mass is suppressed. That is, from the viewpoint that it is preferable to suppress the decrease in the intrinsic viscosity IV at the time of melting to less than 20% in order to solve the problems such as the breaking of the stretching process that occurs based on the decrease in the intrinsic viscosity IV caused by the hydrolysis. The polyester before melting is usually dried until the water content becomes 50 ppm or less. However, such drying requires, for example, conditions at 80 ° C. for 3 hours. Furthermore, since the dried polyester is melt-extruded after being allowed to cool, most of the heating energy in the drying process is melt-extruded. Lost without being used in the process. Therefore, in the present invention, when a bent type twin screw extruder is used, the effect of using substantially undried polyester is not only the production efficiency but also the industrial value from the viewpoint of energy saving. is there.

  In addition, when substantially undried polyester is used, recovered polyester such as slit film discharged from the film production process is also properly pulverized without drying and then directly melt extruded with the undried new polyester. It can be performed.

  The amount of the cyclic trimer deposited on the surface of the polyester film is a characteristic related to the polyester layer formed by mixing the polyester (A).

  In the present invention, in the case of a film having a single layer structure using one extruder, it is necessary that the intrinsic viscosity and the amount of terminal carboxyl groups are within the above ranges with respect to the whole film.

  In the case of a film having a laminated structure by coextrusion, it is preferable that the intrinsic viscosity and the amount of terminal carboxyl groups are within the above ranges with respect to the outermost polyester layer constituting the film.

  In order to make the cyclic trimer amount in the outermost polyester layer obtained by the production method of the present invention a specific range, for example, shortening the residence time of the polyester component in the extruder in the extrusion process of the polyester chip, etc. This is desirable from the viewpoint of the manufacturing method. Moreover, you may obtain the polyester film which consists of a polyester layer whose cyclic | annular trimer amount is a specific range by forming the polyester chip | tip of the amount of low cyclic | annular trimers. In addition, in the production of a film, when a recycled material that has undergone a melting step is blended, the amount of cyclic trimer derived from the polyester layer tends to increase outside the specified range. It is preferable that a large amount is not blended in the melt extruder for forming the layer, and even if blended, it is 40% by weight or less, more preferably 20% by weight or less.

  In the present invention, a coating layer is formed on one side or both sides of the film in order to impart adhesiveness, antistatic property, slipperiness, releasability, etc. to the film in or after the stretching step, or corona treatment. It is also possible to perform a discharge treatment such as.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist of the present invention. In addition, the measurement and evaluation method of various physical properties of a film are shown below.

(1) Amount of terminal carboxyl group (equivalent / ton)
After pulverizing the polyester chip, the sample was dried at 140 ° C. for 15 minutes in a hot air dryer, cooled to room temperature in a desiccator, 0.1 g was accurately weighed and collected in a test tube, and 3 ml of benzyl alcohol was added. The solution was dissolved at 195 ° C. for 3 minutes while blowing dry nitrogen gas, and then 5 ml of chloroform was gradually added and cooled to room temperature. One to two drops of phenol red indicator were added to this solution, and titrated with 0.1 (N) benzyl alcohol solution of caustic soda while blowing dry nitrogen gas, and when the color changed from yellow to red, the procedure was terminated. . Further, as a blank, the same operation was carried out without a polyester resin sample, and the acid value was calculated by the following formula.

Acid value (equivalent / t) = (A−B) × 0.1 × f / W
[Where A is the amount of benzyl alcohol solution of 0.1N caustic soda required for titration (μl), B is the amount of benzyl alcohol solution of 0.1N caustic soda required for titration with blank (μl) , W is the amount (g) of the polyester resin sample, and f is the titer of the benzyl alcohol solution of caustic soda of 0.1 (N)]
The titer (f) of a 0.1 (N) caustic soda benzyl alcohol solution was obtained by collecting 5 ml of methanol in a test tube, adding 1 to 2 drops of phenol red ethanol solution as an indicator, and adding 0.1 (N ) Titration with 0.4 ml of a benzyl alcohol solution of caustic soda, and then adding 0.2 ml of 0.1 (N) aqueous hydrochloric acid solution having a known titer as a standard solution, and adding 0.1 (N) again. N) The solution was titrated with the benzyl alcohol solution of caustic soda to the discoloration point (the above operation was performed under blowing of dry nitrogen gas). The titer (f) was calculated by the following formula.

  Titer (f) = Titer of 0.1N hydrochloric acid aqueous solution × Sample volume of 0.1N hydrochloric acid aqueous solution (μl) / Titration volume of 0.1N sodium hydroxide in benzyl alcohol (μl)

(2) Intrinsic viscosity (dl / g)
After pulverizing the polyester chip, the polyester chip is dissolved in a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), and using a capillary viscometer, the flow time of the solution having a concentration of 1.0 g / dl and the solvent Only the flow down time was measured, and the intrinsic viscosity was calculated from the time ratio using the Huggins formula. At that time, the Huggins constant was assumed to be 0.33.

(3) Quantification of catalyst-derived element A polyester chip was pressed in an environment of 280 ° C. and then cooled to obtain a sample. Using an X-ray fluorescence analyzer (model “XRF-1800” manufactured by Shimadzu Corporation), the amount of elements in the film was determined by single-sheet measurement under the conditions shown in Table 1 below. In the case of a laminated film, the content of titanium element (Ti), phosphorus element (P), antimony element (Sb), and manganese (Mn) with respect to the polyester chip is measured by melting the film and molding it into a disk shape. It was measured.

(4) Amount of cyclic trimer in polyester chip A sample of 10 g was dried in an inert oven (“IPHH-201 type” manufactured by ESPEC) for 2 hours at 160 ° C. under a nitrogen gas flow of 50 NL / min. 4.0 mg is precisely weighed and dissolved in 2 ml of a mixed solvent of chloroform / hexafluoroisopropanol (volume ratio 3/2), further diluted by adding 20 ml of chloroform, precipitated by adding 10 ml of methanol, and subsequently. The filtrate obtained by filtration was evaporated to dryness and then dissolved in 25 ml of dimethylformamide, and the cyclic trimer (cyclotriethylene terephthalate) in the solution was subjected to liquid chromatography (“LC-10A” manufactured by Shimadzu Corporation). Quantified.

(5) Amount of cyclic trimer on the surface of the polyester film A4 size Kent paper is combined with the polyester film to be heat-treated, and the corners are clipped with a Zem clip or the like to stop the Kent paper and the polyester film. At that time, in the case of a laminated polyester film, the surface containing the polyester (A) is arranged outside. Under a nitrogen atmosphere, the polyester film is left in an oven at 150 ° C. for 90 minutes to perform heat treatment. A square box is formed by folding the heat-treated polyester film so that the upper part is opened and the area of the bottom side is 250 cm ² . In the case of a laminated polyester film, the surface containing the polyester (A) is set to be inside. Next, 10 ml of DMF (dimethylformamide) is placed in the box prepared by the above method, and the DMF is recovered after being left for 3 minutes. The recovered DMF was supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of cyclic trimer in DMF. The film area where DMF was brought into contact with this value was divided by 250 cm ² , and the film surface was circular. Trimer mass (mg / cm ² ). The amount of cyclic trimer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method).

  The standard sample was prepared by accurately weighing the preliminarily prepared cyclic trimer and dissolving it in accurately measured DMF. The concentration of the standard sample is preferably in the range of 0.001 to 0.01 mg / ml.

The conditions for the liquid chromatograph were as follows.
Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: “MCI GEL ODS 1HU” manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm
Evaluation criteria ○: Less than 1 × 10 ⁻⁵ mg / cm ² Δ: 5 × 10 ⁻⁵ to 1 × 10 ⁻⁵ mg / cm ²
×: 6 × 10 ⁻⁵ mg / m ² or more

<Method for producing polyester (1)>
A slurry is prepared using a continuous polymerization apparatus comprising a slurry preparation tank, a two-stage esterification reaction tank connected in series to the slurry preparation tank, and a three-stage melt polycondensation tank connected in series to the second-stage esterification reaction tank. To the preparation tank, terephthalic acid and ethylene glycol were continuously supplied at 865 parts by weight and 485 parts by weight, respectively, and a 0.3 wt% ethylene glycol solution of ethyl acid phosphate was added to the phosphorus atom per 1 ton of the resulting polyester resin. Was added continuously in such an amount that the content became 0.129 mol / resin t, and a slurry was prepared by stirring and mixing. This slurry was subjected to a first stage esterification reaction tank set at 260 ° C. under a nitrogen atmosphere, a relative pressure of 50 kPa (0.5 kg / cm ² ) and an average residence time of 4 hours, and then at 260 ° C. under a nitrogen atmosphere. Then, the mixture was continuously transferred to a second stage esterification reaction tank set at a relative pressure of 5 kPa (0.05 kg / cm ² ) and an average residence time of 1.5 hours to cause an esterification reaction. At that time, a 0.6 wt% ethylene glycol solution of magnesium acetate tetrahydrate is contained as magnesium atoms per 1 t of the obtained polyester resin through an upper pipe provided in the second stage esterification reaction tank. The amount was continuously added in an amount of 0.165 mol / resin t, and 60 parts by weight of ethylene glycol was continuously added through another upper pipe provided in the second stage esterification reaction tank. . Subsequently, when the esterification reaction product obtained above is continuously transferred to the melt polycondensation tank, tetra-n-butyl titanate is added to the esterification reaction product in the transfer pipe with a concentration of titanium atoms. As an ethylene glycol solution with 0.15% by weight and a water concentration of 0.5% by weight, it is continuously added in such an amount that the content as titanium atoms per 1 ton of the obtained polyester resin is 0.084 mol / resin t. However, the first stage melt polycondensation tank set at 270 ° C. and absolute pressure 2.6 kPa, then the second stage melt polycondensation tank set at 278 ° C. and absolute pressure 0.5 kPa, then Continuous transfer to a third stage polycondensation tank set at 280 ° C. and an absolute pressure of 0.3 kPa so that the intrinsic viscosity of the resulting polyester resin is 0.65 (dl / g) Each polycondensation Polyester (1) by adjusting the residence time in the melt and polycondensing it, continuously extracting it into a strand from the outlet provided at the bottom of the polycondensation tank, cooling with water and cutting with a cutter. ) Was manufactured. The amount of terminal carboxyl groups was 12 (equivalent / ton), and the amount of cyclic trimer in the polyester chip was 6800 (ppm).

<Method for producing polyester (2)>
Polyester (1) is used as a starting material, and is continuously fed into a stirring crystallization machine maintained at about 160 ° C. in a nitrogen atmosphere so that the residence time is about 60 minutes. Continuously supplied to a solid phase polycondensation apparatus, and at 215 ° C. under a nitrogen atmosphere, the residence time was adjusted so that the intrinsic viscosity of the obtained polyester resin was 0.82 (dl / g), and solid phase polycondensation was performed. Polyester (2) was obtained. The amount of terminal carboxyl groups was 8 (equivalent / ton), and the amount of cyclic trimer in the polyester chip was 3000 (ppm).

<Method for producing polyester (3)>
100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol are used as starting materials, and tetra-n-butyl titanate is obtained as a catalyst. The amount of titanium atoms per 1 ton of polyester resin is 5 g / resin t. In the reactor, the reaction start temperature was 150 ° C., and the reaction temperature was gradually increased as methanol was distilled off. After 4 hours, the transesterification reaction was substantially terminated. The reaction mixture was transferred to a polycondensation tank and the average particle size 2. An ethylene glycol slurry of 5 μm silica particles was added so that the content of the particles with respect to the polyester was 1.5% by weight, and a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.60 due to a change in stirring power in the reaction tank, and the polymer was discharged under nitrogen pressure to obtain polyester (3). The intrinsic viscosity was 0.60 (dl / g), the terminal carboxyl group amount was 21 (equivalent / ton), and the cyclic trimer amount in the polyester chip was 7000 (ppm).

<Method for producing polyester (4)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, 0.02 part of magnesium acetate tetrahydrate as a catalyst is added to the reactor, the reaction start temperature is set to 150 ° C., and the methanol is gradually distilled off. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.03 part of ethyl acid phosphate to this reaction mixture, it moved to the polycondensation tank, added 0.04 part of antimony trioxide, and performed polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (4). The intrinsic viscosity of the polyester was 0.63 (dl / g), the amount of terminal carboxyl groups of the polymer was 35 (equivalent / ton), and the amount of cyclic trimer in the polyester chip was 8500 (ppm).

<Method for producing polyester (5)>
Polyester (4) was used as a starting material, and solid phase polymerization was performed at 220 ° C. under vacuum to obtain polyester (5). The intrinsic viscosity of the polyester (5) was 0.85 (dl / g), the amount of terminal carboxyl groups of the polymer was 21 (equivalent / ton), and the amount of cyclic trimer in the polyester chip was 5500 (ppm).

<Method for producing polyester (6)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, manganese acetate / tetrahydrate as a catalyst was added so that the manganese element was 105 ppm in the polymer, and the reaction start temperature was 150. The reaction temperature was gradually increased as methanol was distilled off, and the temperature was increased to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. Ethyl acid phosphate was added to this reaction mixture so that elemental phosphorus was 77 ppm in the polymer, then transferred to a polycondensation tank, and antimony trioxide was added so that elemental antimony was 166 ppm in the polymer. A time polycondensation reaction was performed. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 (dl / g) due to a change in stirring power in the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester chip. The polyester was crystallized in a 160 ° C. environment, and then held in a 230 ° C. environment until the amount of cyclic trimer in the polyester chip reached 3000 (ppm). While maintaining the temperature environment, a vacuum state of 5 mmHg was applied and solid phase polymerization was performed to obtain polyester (6). The intrinsic viscosity of the polyester (6) was 0.64 (dl / g), the amount of terminal carboxyl groups of the polymer was 7 (equivalent / ton), and the amount of cyclic trimer in the polyester chip was 3000 (ppm).

Example 1:
The polyester (1) and the polyester (3) mixed at a ratio of 96: 4 are used as raw materials and extruded at a discharge rate of 450 kg / hr and a screw rotation speed of 100 rpm in a twin screw extruder with a diameter of 90 mm. It was melt-extruded at 290 ° C. and rapidly cooled and solidified on a casting drum having a surface temperature set to 40 ° C. using an electrostatic application adhesion method to obtain an unstretched single-layer sheet. The obtained sheet was stretched 3.3 times in the longitudinal direction at 83 ° C., led to a tenter, stretched 3.7 times in the lateral direction at 110 ° C., and heat-set at 220 ° C. The average thickness of the obtained film was 125 μm. The properties and evaluation results of the obtained film are shown in Table 3 below.

Examples 2 and 3:
A polyester film was obtained in the same manner as in Example 1 except that the polyester raw material having the blending ratio shown in Table 2 was used. The properties and evaluation results of the obtained film are shown in Table 3 below.

Example 4:
The polyester (1) and polyester (3) mixed in a ratio of 96: 4 is used as the polyester raw material for the X layer, and the polyester (4) is used as the polyester raw material for the Y layer, and each is supplied to two extruders. After melting at 290 ° C., the X layer is the outermost layer (surface layer), the Y layer is the intermediate layer, and the casting composition cooled to 40 ° C. is a two-and-three layer (XYX) with a thickness composition ratio of X : Y: X = 6.25: 112.5: 6.25 was coextruded and cooled and solidified to obtain a non-oriented sheet. At that time, in order to form the X layer, it was extruded with a vented twin screw extruder having a diameter of 44 mm at a discharge rate of 25 kg / hr and a screw rotation speed of 100 rpm, and in order to form the Y layer, a vent with a diameter of 90 mm was attached. Extrusion was performed with a twin screw extruder at a discharge rate of 225 kg / hr and a screw rotation speed of 50 rpm. The obtained sheet was stretched 3.3 times in the longitudinal direction at 83 ° C., led to a tenter, stretched 3.7 times in the lateral direction at 110 ° C., and heat-set at 220 ° C. The average thickness of the obtained film was 125 μm. The properties and evaluation results of the obtained film are shown in Table 3 below.

Comparative Examples 1 to 3:
In Example 1, a film was obtained in the same manner as in Example 1 except that the polyester raw material in the mixture was changed to the polyester shown in Table 4. The characteristics and evaluation results of the obtained film are shown in Table 4 below. Comparative Example 2 and Comparative Example 3 were not suitable for long runs because of high pressure during extrusion. Further, the amount of cyclic trimer on the film surface is high when the polyester film is formed, although the amount of cyclic trimer in polyester (5) is higher than that of polyester (1). Since the intrinsic viscosity of the film is high, the amount of shear heat generation in the extruder is large, resulting in a situation in which molecular cutting tends to occur, and it is considered that the cyclic trimer in the film has increased.

  The film obtained by the production method of the present invention can be suitably used for, for example, a touch panel.

Claims (2)

A polyester layer containing 60% by weight or more of a polyester resin (A) having a terminal carboxyl group amount (AV) of 20 equivalent / t or less and an intrinsic viscosity (IV) of 0.65 dl / g or less is melt-extruded to form a polyester layer. A method for producing a polyester film, comprising molding. 2. The method for producing a polyester film according to claim 1, wherein the polyester layer according to claim 1 is at least one outermost layer.